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Sustainable Agriculture Research and Education in the Field: A Proceedings (1991)

Chapter: PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION

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Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

PART FIVE

Research and Education in the Northeastern Region

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×
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Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

18

Long-Term, Low-Input Cropping Systems Research

Rhonda R. Janke, Jane Mt. Pleasant, Steven E. Peters, and Mark Böhlke

One of the most challenging areas of research within the mandate of low-input sustainable agriculture (LISA) involves long-term cropping system studies. Agricultural scientists are continually faced with a dilemma when implementing research of this nature. The problem is how to conduct component research that tests a specific hypothesis about one or two factors (e.g., nitrogen fertility or weed control) while maintaining the realism and complexity of the cropping systems described in whole-farm comparisons and case studies. One of the myths that dominated the research community in 1981 was that LISA-type cropping systems were nothing more than conventional systems without the use of chemicals (Harwood, 1984). As a result, component research at that time “proved” that these systems were inferior to the conventional management approach. Experiments designed with this primary assumption (bias) failed to take into account the fact that chemical usage is only one of many factors involved in designing the efficient, well-structured, integrated, and biologically stable systems that have been found on many commercial organic farms (National Research Council, 1989; U.S. Department of Agriculture, 1980). The interactions among the components of an efficient farm enterprise, such as the use of cover crops and animal manures, biological nitrogen fixation, nutrient uptake and release rates, weed dynamics, disease and insect suppression, and the rotation effect, are poorly understood (Harwood, 1985). Replicated and controlled settings are needed to explore, evaluate, and comprehend these vital processes. In addition to answering questions about basic biological processes, well-researched model cropping systems provide valuable agronomic and economic information for farmers, extension agents, and agribusinesses.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

This chapter describes three studies of long-term cropping systems currently being conducted in the United States. Several other studies are ongoing at other locations (California, Nebraska, Ohio, and Michigan, to name a few). The three studies described in this chapter are located in New York and Pennsylvania and received funding from the LISA program of the U.S. Department of Agriculture (USDA) for the 1988 and 1989 growing seasons. Some of the agronomic and economic results from these studies are highlighted, although two of the three studies were established in 1988, and from a pragmatic point of view, these data should be considered preliminary results.

This raises a question of concern for researchers involved with long-term studies: How are sustainable funding sources for low-input sustainable agriculture research obtained? If it takes between 5 and 10 years to begin to get useful data from experiments (posttransition period), who should be asked to bear the cost of supporting this research? Private industries, by nature, tend to support research that is usually geared only toward product development and testing. Public research funds are mandated for research that benefits the public at large. Low-input sustainable agriculture now has the support of the public because of the increasing awareness of the negative environmental effects of some conventional agricultural practices, including groundwater and surface water pollution and soil erosion. The public has also become more concerned about food quality and safety. It is clear that long-term research is needed to develop and improve upon options available to farmers. However, the public funds allocated to sustainable agriculture (the LISA program of USDA) continues to flow in small, 1-year grants. This is a contradiction that must be resolved.

THE RODALE FARMING SYSTEMS TRIAL

A long-term study was initiated in 1981 at the Rodale Research Center in southeastern Pennsylvania to examine the process of converting from a conventional to a low-input/organic cropping system. Three representative cropping systems were designed:

  1. A low-input (i.e., low purchased input) system with animals (LIP-A) that simulates a crop and livestock farm (typical of farms in Pennsylvania and several other regions of the country) uses a 5-year rotation that includes corn grain, soybeans, small grains, legume hay, and corn silage. Animal manure is applied prior to each crop of corn to supplement the legume nitrogen from the previous hay or soybeans (Table 18-1).

  2. The low-input cash grain (LIP-CG) system is based on the assumption that a cash crop is needed each year for cash flow and that no animal manure is available.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 18-1 Five-Year Rotations for the Farming Systems Trial, Rodale Research Center

 

Crops

System

Year 1

Year 2

Year 3

Year 4

Year 5

Low-input with animals

Wheat/alfalfa + red clover*

Alfalfa + red clover

Corn

Soybeans

Corn silage

Low-input cash grain

Barley/soybeans

Wheat/red clover*

Corn

Barley/soybeans

Wheat/red clover*

Conventional cash grain

Corn

Soybeans

Corn

Soybeans

Corn

* Alfalfa and/or red clover was frost seeded (broadcast seeded in March) into wheat.

Soybeans were relay planted (drilled into a small grain) into spring barley.

  1. The conventional (CONV) rotation of corn and soybeans is grown with purchased fertilizer, herbicides, and insecticides applied at rates as provided in guidelines of Pennsylvania State University (University Park, Pennsylvania).

The low-input (LIP) rotations rely on crop rotation, cover crops, relay cropping, and mechanical cultivation for weed control and only on green manures and animal manures as nitrogen sources. Each of the three crop rotations was started at three different points in the rotation, for a total of nine treatments. These treatments were replicated eight times in a split-plot, randomized complete block design. Whole plots are 60 × 300 feet, and subplots are 20 × 300 feet. Cropping systems (LIP-A, LIP-CG, or CONV) were assigned to whole plots, which were split by rotation entry point. More detailed descriptions of and results from this experiment can be found in the literature (Andrews et al., 1990; Culik, 1983; Harwood, 1984, 1985; Liebhardt et al., 1989; Peters et al., 1988; Radke et al., 1988).

During the biological transition period (1981 to 1984), that is, during the process of converting from CONV to LIP methods, a change in the equilibrium between soil processes and plant growth was anticipated and observed. Evidence that supports this includes the fact that both LIP systems (animal and cash grain) had lower corn yields than the CONV cropping system did in 1981 to 1984 (Figure 18-1), whereas all three systems have had similar corn yields since then. This is attributed to a lack of nitrogen in the soil that was available to plants in the LIP systems during the transition years, as reflected in corn ear leaf nitrogen analysis (Figure 18-2), but there has

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

been an adequate supply of nitrogen from 1985 to the present. Excessive weed growth in some years may have also limited crop yield and may have been compounded by the lack of nitrogen, although no consistent pattern of weed increases, decreases, or species shifts was apparent from the transition period data. Annual weeds dominate in the LIP rotations, and perennials dominate in the CONV system, partly because of herbicide selectivity.

Soybean yields were similar in all three systems during the transition years (Liebhardt et al., 1989), and small-grain and hay yields compared favorably to county averages (Peters et al., 1988). Thus, corn was the only crop that appeared to be limited during this biological transition period. Conclusions about the best way to go through the transition agronomically (begin the rotation with a small-grain and cover crop or soybeans) were verified in an economic analysis (Duffy et al., 1989) of the transition years. When the rotation begins with a small grain and legume or soybeans, the result is a greater return to land and management than that from “cold turkey” corn in the LIP systems. If higher crop prices because of federal government price support programs are not factored in, the order of average returns from each system (combining all rotation entry points) was as follows: LIP-A > CONV > LIP-CG. The CONV system was the most profitable if the government price support program for corn was included. However, because rotation entry point was a significant factor, the most profitable LIP-CG treatment resulted in a higher average annual net return than that from the least profitable CONV treatment.

FIGURE 18-1 Average corn yields from the farming systems trial from 1981 to 1984 (during conversion) versus those from 1985 to 1988 (postconversion).

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 18-2 Average tissue nitrogen content of corn ear leaves at the time of silking from the farming systems trial for 1981 to 1984 (during conversion) versus that for 1985 to 1988 (postconversion).

Initially called the conversion experiment, the study was renamed the farming systems trial in 1986. Emphasis shifted toward an assessment of the long-term reliability of LIP practices. The four major objectives are (1) to compare crop performance in the three cropping systems; (2) to compare the economic viability of these rotations and input regimes; (3) to test the sustainability, regenerative capabilities, and environmental impact of the LIP approaches by monitoring soil chemical and physical properties, weed pressure, and nitrogen cycling processes over time; and (4) to continue to encourage active collaboration with the agricultural research community for increasing understanding of the mechanisms of soil and plant processes in a biologically complex environment.

Total biomass production and grain yields have essentially been the same in all systems since 1985. Nitrogen does not currently limit corn yield in any system, as determined by the ear leaf tissue test (Table 18-2) and by extensive testing of soil nitrate nitrogen levels during the growing season (Figure 18-3A and B). Similar levels of nitrogen are supplied to corn crops in each rotation, amounting to 130 pounds (lbs) of nitrogen per acre as fertilizer in the CONV rotation, an average of 75 lbs of nitrogen per acre in the top growth of the clover before plowing in early May in the LIP-CG rotation, and an average of 205 lbs of nitrogen in beef manure per acre applied to the LIP-A system from 1986 to 1990. Most agronomic literature advises that only 50 percent of the nitrogen in the beef manure is available

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 18-2 Corn Yield, Tissue Nitrogen Content of Ear Leaves at Silking, and Weed Biomass for 1988 and 1989, Farming Systems Trial, Rodale Research Center

Treatment

Corn Yield (bu/acre)

Tissue Nitrogen (% N)

Weed Biomass (lbs/acre)

1988

LIP-A*

110a

2.86a

900a

LIP-CG

109a

2.96a

449b

CONV (soybeans)

104a

2.79a

88c

CONV (corn)

85b

2.74a

250bc

1989

LIP-A

124ab

2.64a

1,343a

LIP-CG

111c

2.72a

100c

CONV (soybeans)

130a

2.87a

251bc

CONV (corn)

116bc

2.86a

486b

NOTE: LIP, low input; A, animals; CG, cash grain; CONV, conventional.

* Previous crop for LIP-A treatment was 2-year-old red clover-alfalfa mixture; for LIP-CG was a 1-year-old red clover stand; and CONV treatments followed either soybeans or corn.

Letters designate statistical differences at the p < 0.05 level by using analysis of variance (performed with Statistical Analysis System software) and Duncan's multiple range test. The Duncan letters should be read within a year, within a column only.

A plus/minus weed study was superimposed on the experiment to determine whether ambient weed levels caused yield suppression. Only the LIP-A treatment in 1988 showed statistically significant yield reduction in the “plus” weed subplot (yield was about 80 percent that of the hand-weeded control plot).

to crops the year of application, with a fraction of that amount of nitrogen being available in subsequent years. The literature also indicates that the legume nitrogen is only available to corn in the long term and not the short term, but data from these studies indicate that no supplemental nitrogen fertilizer is currently needed to meet the nitrogen needs of either the LIP-A or the LIP-CG systems.

Weeds are often more abundant in the LIP systems than they are in the CONV systems, but weeds have reduced the corn yield in only two systems since 1986. Corn in the LIP-CG system in 1986 (data not shown) and the corn in the LIP-A system in 1988 showed statistically significant yield reductions (Table 18-2) in unweeded versus hand-weeded subplots. The highest yields in 1988 were from corn in the LIP-A system, despite the weeds. The critical weed threshold levels change from year to year, depending on weather and growing conditions. Over 1,300 lbs of weeds (dry weight) per acre did not decrease the corn yield in the LIP-A system in 1989, probably because rainfall was plentiful and timely and moisture was not limiting (it was limiting in 1988).

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 18-3 Soil nitrate notrogen levels in the farming systems trial at the Rodale Research Center in (A) 1988 and (B) 1989

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

Soil biology data (Doran et al., 1987; Fraser, 1984; Werner, 1988) indicate that the LIP systems have greater microbiological activity and a greater abundance of many microarthropods. The microbial activity is attributed more to the diversity of crops in the rotation, especially the legume cover crops and hay, and to the application of animal manure in the LIP-A system than it is to the absence of pesticides and chemical fertilizers. This increased biological activity may partially account for preliminary results from 15N studies (Harris et al., 1989), which indicate that less nitrogen is lost from the LIP-CG system than is lost from the CONV system and that more nitrogen is retained in the soil in the LIP-CG system. Preliminary work by a graduate student at Ohio State University (Columbus) will help to determine the role of various fractions of organic matter in holding onto the nitrogen, and sampling of vesicular-arbuscular mycorrhizae by a researcher of the Agricultural Research Service of USDA in Wyndmoor, Pennsylvania, will help to determine the role of these organisms in nutrient cycling and availability of nutrients of plants.

An approximation of a whole-farm analysis with the yields from 1981 to 1989 was made by using FINPACK farm management software to simulate a 750-acre Maryland farm (Hanson et al., 1990). In that analysis only the CONV and the LIP-CG systems were compared, and similar average annual profits over the 9-year period were found without the government price support program ($29,891 for the CONV system versus $27,614 for the LIP-CG system). However, with the government price support program for corn (requiring base acres and set-asides) the CONV system averaged $39,193 per year. The farmer of the LIP-CG system would have averaged $32,464 if the same set of price supports was used for corn, wheat, and barley, but this is a fictitious scenario because this farmer would not have been in compliance (would not have met the base acre cross-compliance requirements for wheat and barley). Another interesting result of the 1981 to 1989 economic comparison was that the farmer of the LIP-CG system experienced less fluctuation in annual income. The standard deviation in annual income over the 9-year period was $16,985 compared with that of the CONV farmer who did not participate in the government price support program (standard deviation, $37,811) or the CONV farmer who did participate in that program (standard deviation, $26,416).

None of these results would be possible if this were a 2-year or even a 5-year trial. In this trial, biological processes became most interesting after the initial 5-year transition period, and economic analyses of long-term performances and variabilities in income are possible now that the trial is entering its tenth cropping season. Ironically, this experiment was supported by the private sector (Rodale Press) for the first 7 years, and USDA funding from the LISA program of USDA during 1988 and 1989 has supplied only a fraction of the total cost of conducting the experiment, an-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

alyzing the data, supporting the work of collaborators, and presenting the results. Funding from the LISA program of USDA has, however, allowed the investigators involved in the study described here to strengthen collaborative relationships with researchers at Cornell University (Ithaca, New York), and has facilitated the initiation of the Cornell cropping systems experiment. Soil scientists from Cornell University have conducted a detailed taxonomic description of the soils at the Rodale site (Waltman and Scott, 1989) and are involved in measuring the physical properties of the soil (such as hydraulic conductivity, by Harold van Es, Soil Science Department, Cornell University, Ithaca, New York) and characterizing roots (Rich Zobel, USDA, Ithaca, New York).

THE CORNELL CROPPING SYSTEMS EXPERIMENT

A long-term experiment was initiated at Cornell University to address concerns specific to farmers in that climatic region. Dairy farming is the dominant agricultural enterprise in much of New York State and other states in the Northeast. The growing season is shorter and soils are colder than soils in Pennsylvania. Corn silage is more common than corn grain in New York, and farm rotations often include alfalfa. The Cornell experiment was designed to compare standard practices with alternative strategies that reduce the use of agrichemicals for corn silage production. Alternative practices include (1) ridge tillage, (2) manure substitution for inorganic nitrogen, (3) interseedings of cover crops, and (4) band application of herbicide or cultivation for weed control. A total of 10 cropping systems (Table 18-3) are being compared, with three weed control regimes imposed on each cropping system. The experiment is being conducted at two sites (Aurora and Mt. Pleasant research farms), and there are five replications at each site.

The entire project includes more than 30 people, including eight farmers, six extension agents, and six faculty members of Cornell University with primary extension responsibilities (see Mt. Pleasant [1990] for a list of participants). In addition to the long-term trials initiated on the research farms, field-scale trials are being conducted on six New York dairy and cash-grain farms. These trials are comparing several practices that reduce fertilizer or pesticide use in corn to conventional farming practices. Faculty members from several disciplines, including soil and crop science, entomology, plant pathology, and plant breeding, contribute significant time and expertise to the project.

Although 1989 was the second year of funding from the LISA program for this project, it was the first year that all treatments were established at both sites. The 1988 growing season was used to prepare the sites, perform the ridging operations, and plant cover crops. Corn silage yields for the

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 18-3 Cropping Systems Treatments, Mt. Pleasant and Aurora Research Farms, Cornell University

Treatment

Cropping System

1

Corn-corn-alfalfa-alfalfa*.

2

Corn-oats/alfalfa-alfalfa-alfalfa*

3

Continuous corn

4

Continuous corn + manure

5

Continuous corn (ridge till)

6

Continuous corn (ridge till) + manure

7

Continuous corn (ridge till) + interseeded red clover

8

Continuous corn + interseeded red clover

9

Continuous corn (ridge till) + interseeded ryegrass

10

Continuous corn + interseeded ryegrass

* All four rotation sequence entry points are represented in the experiment.

All treatments were subjected to three weed control regimens in a split-plot design: (a) cultivation only, (b) banded herbicide (10-inch over row), and (c) broadcast herbicide. For rates and compounds, see J. Mt. Pleasant. 1990. Alternative Cropping Systems for Low-Input Agriculture in the Northeast. Lisa Program Progress Report. Ithaca, N.Y.: Cornell University. Mimeograph.

Manure supplied the major portion of the recommended nitrogen. For all other treatments, inorganic fertilizers were used.

1989 growing season showed the effectiveness of several practices for reducing inputs while maintaining yields and protecting soil and water resources (Table 18-4). For example, banded application of herbicides combined with one cultivation reduced herbicide use by more than 60 percent compared with broadcast application. Weed levels in the banded herbicide application plus cultivation plots were the same or slightly higher than those in the broadcast application plots (Table 18-5), but corn yields were equal to or higher than those from the broadcast herbicide plots (Table 18-4). The plots that received no herbicides had higher weed levels than the band or broadcast applications did, and the yields from both sites were significantly lower than those from plots that were treated with herbicide. The yield reduction, however, was less than 10 percent, and it remains to be seen whether that reduction is economically significant (Mt. Pleasant, 1990). Because of the wet weather conditions during the 1989 growing season, only one cultivation was performed on the plots that were not treated with herbicides. Greater efficacy of the cultivation treatment is anticipated in future years as operator experience with the cultivator improves and if more favorable weather conditions allow more timely operations.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

The use of red clover and ryegrass interseeding was successfully demonstrated on several field-scale, on-farm trials in New York. Ground cover from the interseedings ranged from 11 to 37 percent in mid- to late summer, with no effect (negative or positive) on corn yields (Mt. Pleasant, 1990). Interseedings could potentially reduce nitrate leaching in the fall, provide soil cover through the winter, and contribute substantial amounts of organic matter and nitrogen to the cropping system the following year. There is also some indication that interseeding may promote weed suppression (i.e., ridge-till plots at the Mt. Pleasant site in 1989; see Mt. Pleasant [1990]).

TABLE 18-4 Effects of Cropping System and Weed Control Treatments on Corn Silage Yields and Weed Levels, Mt. Pleasant Research Farm, Cornell University, 1989

Weed Control

Cropping System

Cultivated

Band

Broadcast

Mean

Corn Silage Yield (tons/acre at 70% moisture)

Conventional till

11.92

13.73

12.22

12.62

Conventional till + manure

8.15

10.36

10.73

9.75

Ridge till

6.63

9.35

9.63

8.53

Ridge till + manure

4.15

5.10

8.27

5.84

Ridge till + RC

13.85

12.94

10.47

12.42

Conventional till + RC

12.98

14.87

11.95

13.27

Ridge till + RG

12.01

12.18

10.55

11.58

Conventional till + RG

12.53

14.41

13.20

13.38

Mean

10.83

11.83

11.22

 

Weed Cover (%)

Conventional till

71.8

21.2

0.0

31.0

Conventional till + manure

78.6

23.4

0.4

34.1

Ridge till

120.0

73.2

6.2

66.5

Ridge till + manure

73.0

67.0

2.4

47.5

Ridge till + RC

47.6

23.0

6.2

25.6

Conventional till + RC

73.6

20.2

0.8

31.5

Ridge till + RG

62.2

42.0

15.2

39.8

Conventional till + RG

71.0

21.0

0.4

30.8

Mean

73.3

31.0

2.9

 

NOTE: RC, red clover interseeding; RG, ryegrass interseeding. Analysis of variance values for corn silage yields: system, p = 0.0001; weed control, p = 0.0079; system × weed control interaction, p = 0.0005. Analysis of variance values for weed levels: system, p = 0.0001; weed control, p = 0.0001; system × weed control interaction, p = 0.0001.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 18-5 Effects of Cropping System and Weed Control Treatments on Corn Silage Yields and Weed Levels, Aurora Research Farm, Cornell University, 1989

Weed Cover (%)

 

Weed Control

Cropping System

Cultivated

Band

Broadcast

Mean

 

Corn Silage Yield (tons/acre at 70% moisture)

Conventional till

23.40

24.65

25.15

24.40

Conventional till + manure

20.14

20.85

20.36

20.45

Ridge till

22.47

24.10

24.14

23.57

Ridge till + manure

21.75

23.86

22.62

22.74

Ridge till + RC

23.06

24.09

24.33

23.83

Conventional till + RC

24.71

25.31

22.88

24.30

Ridge till + RG

22.66

24.54

23.61

23.60

Conventional till + RG

21.37

23.28

22.72

22.46

Mean

22.62

23.92

23.59

 
 

Conventional till

8.6

5.4

3.3

5.8

Conventional till + manure

20.1

4.3

0.6

8.2

Ridge till

8.8

3.1

0.2

4.0

Ridge till + manure

4.4

1.2

0.8

2.1

Ridge till + RC

7.9

5.0

0.6

4.5

Conventional till + RC

11.0

5.1

4.5

6.9

Ridge till + RG

8.6

7.2

1.8

5.9

Conventional till + RG

10.4

4.0

10.1

8.2

Mean

9.9

4.1

2.8

 

NOTE: RC, red clover interseeding; RG, ryegrass interseeding. Analysis of variance values for corn silage yields: system, p = 0.1220; weed control, p = 0.0002; system × weed control interaction, p = 0.5796. Analysis of variance values for weed levels: system, p = 0.1559; weed control, p = 0.0001; system × weed control interaction, p = 0.0072.

This result was also observed in some early studies on cover crop interseeding conducted by the Rodale Research Center (Palada et al., 1982). Corn also appears to benefit from cover crop interseeding established in the previous year. In 1989, corn at the Mt. Pleasant site showed a significant positive response to cover crops that were established in 1988. This response was not observed in a previous study of interseeded systems in New York (Scott et al., 1987), because interseeding was not examined under different tillage practices or under various levels of weed control. It is hypothesized that changes in soil structure or effects on weed infestation were responsible for the corn yield response in the long-term study.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

Other results from 1989 indicate that corn yields were lower in plots that received manure than they were in plots that received sidedressed inorganic nitrogen. In 1989, corn response to manure was not consistent with the large body of data from previous research on crop response to manure at Cornell University. Apparently, the very wet spring in the Northeast was largely responsible for the reduced nitrogen availability from manure in 1989. The yield for ridge-tilled corn was less than that for conventionally tilled corn when manure was the primary nitrogen source, but yields were the same for both tillage systems that received inorganic nitrogen. Ridge tillage is believed to be a promising reduced-tillage system for New York farmers, because soil in the ridge may warm up faster than soil in a high-residue, flat, no-till system.

Other interesting results from the Cornell study show that there are significant interaction effects of tillage system and cover crops with corn pests. For example, corn eyespot disease was significantly higher in ridge-till treatments compared with those in conventional-till treatments (17.5 versus 0.7 infected plants per 200 square feet). Slug feeding was higher in plots with interseeded cover crops, with an average of 15 plants per 200 square feet showing damage compared with 9 plants per 200 square feet on land without cover crops. However, in 1989 neither of these pests was above the economic threshold level. The interactions of pests with various components of cropping systems are best understood and described in long-term experiments of cropping systems rather than in shorter-term trials, in which these interactions may not be exhibited.

The net value of this experiment as a long-term cropping systems trial has already become apparent during the first year after its establishment. For example, the effects of tillage and interseedings in corn at some sites were contrary to the effects found in past research. This result suggests that examination of cultural practices as part of a cropping system may yield different conclusions than those obtained from single-factor experiments. In addition, organic sources of nitrogen (animal manure) did not always perform as predicted from past research and experience. Nitrogen mineralization from organic nitrogen sources is highly dependent on soil and climatic conditions. The ability to use organic sources of nitrogen efficiently is limited because the processes that control nitrogen mineralization and the cycling of nitrogen within the soil-crop system are not fully understood, especially in new or novel tillage systems. Also, changes in weed control practices affect other pests (disease and insect) as well as the physical properties of the soils. The research at Cornell University has begun to identify and record the complex web of interactions that occurs within a cropping system. It is the first step toward managing that cropping system with greater efficiency.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×
THE RODALE LOW-INPUT, REDUCED-TILLAGE EXPERIMENT

This long-term experiment was initiated in 1988 at the Rodale Research Center to determine the feasibility of reduced-tillage alternatives to the moldboard plow. Reduced-tillage options include chisel plow/disk (some residue left on the surface after tillage), ridge-tillage (no primary tillage but ridge tops cleared of residue at the time of planting), and no-tillage (no primary tillage and all residue left on the soil surface) (Figure 18-4). A mixed-tillage regime is also included in the design. In this treatment the primary tillage method is determined on a year-to-year basis, depending on the presence of weeds and the crop to be planted. The study emphasizes the energy and economic implications of various cropping systems as well as changes in the chemical and physical properties of the soil, weed species diversity and population shifts, and crop growth and yield (Vargas et al., 1989). This is one of the few experiments in the United States that is evaluating the feasibility of no-till crop production without the use of herbicides.

Three cropping systems are compared in Table 18-6. A CONV (recommended rates of fertilizers and pesticides) rotation of corn and soybeans is compared with two different LIP rotations. Both LIP rotations rely primarily on cover crops for nitrogen supply and weed control in the no-till system and do not include pesticides. One LIP rotation (LIP-1) is being run parallel to the CONV corn-soybean rotation and includes cover crops prior to corn and soybeans that are relay cropped into small grains. The relay crop consists of spring barley drilled in early spring, followed by soybeans planted into the tillering barley in May. The barley is harvested for grain in July, and the soybean seed is harvested in the fall at the same time that the CONV soybeans are harvested. The second LIP rotation (LIP-2) is a 4-year rotation with corn and soybeans as the principal crops, but 1 year of a small grain-legume mixture is added to diversify the rotation.

FIGURE 18-4 Experimental design for the low-input (LIP), reduced-tillage experiment at the Rodale Research Center. Four tillage levels × three cropping system regimens resulted in 12 treatments. A thirteenth treatment examined a mixed tillage regimen that was run parallel to LIP-1.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 18-6 Crop Rotation Sequence for the Low-Input, Reduced-Tillage Experiment, Rodale Research Center

Treatment

Year 0, 1987

Year 1, 1988

Year 2, 1989

Year 3, 1990

Year 4, 1991

CONV

Corn

Soybeans

Corn

Soybeans

Corn

LIP- 1

Corn

Barley/soybeans

Hairy vetch/corn

Barley/soybeans

Hairy vetch/corn

LIP-2

Corn

Hairy vetch + rye/corn

Wheat/soybeans

Oats/Berseem clover

Hairy vetch/corn

NOTE: CONV, conventional; LIP, low input.

The field plots are 40 feet wide and 100 feet long, and only the center section (20 × 80 feet) is used for data collection. This center area is subdivided into two areas; half is designated for within-season sampling, and half is designated for final yield determinations, to minimize the impact of sampling on yield determinations and to plan space for trials superimposed by collaborators over the life of the experiment. There is potential for some plot-to-plot interaction effects from some pests (insects, diseases, weeds) but not others, and a combination of sampling only the plot centers and knowledge of the pest species' ecology will minimize errors in pest data interpretation. The 13 treatments are replicated six times in a randomized complete block design. Tillage regimes within each cropping system can be compared every year. In all years, corn and soybeans can be compared between the CONV and the LIP-1 cropping systems, and in years 4, 8, 12, and so on, corn will be present in all three cropping systems for across-system comparisons.

Abnormally dry weather in 1988 greatly reduced the yields, regardless of the cropping system or tillage regime that was used. The moldboard plow regime achieved the highest yields, the chisel/disk and ridge-till regimes were intermediate, and the no-till regime, regardless of cropping system, had the lowest yields (Peters et al., in preparation). In the CONV systems, soybean yields averaged 36 bushels/acre (bu/acre) and ranged from 47 (moldboard plow) to 20 (no-till) bu/acre. In the LIP-1 cropping system, spring barley yields averaged 42 bu/acre, but the relay-cropped soybeans failed to produce any yield because of the drought. The corn in the LIP-2 cropping system yielded between 44 (moldboard plow) and 0 (no-till) bu/acre. The failure of the hairy vetch and competition for moisture from the rye contributed to the agronomic and economic failure of this system in 1988.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

The most noteworthy result from 1989 was that corn that was no-till planted in the mixed-till regime yielded as much as corn in the moldboard plow regime did and was not significantly different from the yield in the best-yielding CONV corn treatments (Table 18-7). Cover crop establishment in the strict no-till system was difficult in 1988, resulting in a poor corn crop in 1989. However, in the mixed-till system, in which plowing was used to establish hairy vetch, it was possible to plant corn by the no-till method without herbicides, and it was found to be the most profitable treatment in 1989 (Wes Musser, Agricultural Economics Department, The Pennsylvania State University, University Park, personal communication of preliminary analysis, 1990). Corn in the strict no-till system (i.e., the LIP-1 no-till regime) was deficient in nitrogen, and the poor cover crop stand in the no-till treatment did not provide adequate weed suppression. Weed control in the other LIP-1 systems was adequate and was not statistically different from the weed control achieved in the CONV cropping system with herbicides (Table 18-7). The lesson in all of this is that good cover crop establishment is essential for reduced-tillage and especially for no-till, LIP rotations to work. It was also found that in a strict, multiyear, no-till system, the establishment of cover crops is difficult. This was not known before this experiment was conducted,

TABLE 18-7 Corn Grain Yield, Percent Nitrogen in Ear Leaf, and Weed Biomass from the Low-Input, Reduced-Tillage Experiment, Rodale Research Center, 1989

Treatment

Grain Yield (bu/acre)

Ear Leaf (% N)

Weed Biomass (lbs/acre)

CONV

Plow

150a*

3.16ab

173de

Chisel

112c

3.24a

372bcde

Ridge till

131abc

3.20a

194de

No-till

147a

3.20a

352bcde

LIP-1

Plow

129abc

3.09abc

144de

Chisel

130abc

2.86cd

17e

Ridge till

117bc

2.81d

121de

No-till

63d

2.12e

1,318a

Mixed till

140ab

2.91bcd

234cde

NOTE: CONV, conventional; LIP, low input.

* Duncan's multiple range test was performed by analysis of variance using Statistical Analysis System software; comparisons are within columns.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

because hairy vetch was used only in short-term experiments to determine, for example, the optimal date of corn planting and equipment needs.

A more detailed look at the hairy vetch showed that hairy vetch germination appeared to be adequate in all treatments, but subsequent slug feeding in the high-residue plots (chisel/disk, ridge-till, and no-till) resulted in diminished hairy vetch stands. Large differences were measured in the spring nitrogen contributions from the aboveground biomass of hairy vetch; 260 lbs/acre in the moldboard plow and mixed-till system, 132 lbs/ acre in the chisel/disk system, 89 lbs/acre in the ridge-till system, and 49 lbs/acre in the no-till system. In the spring of 1989, the mixed-till regime and the no-till system were both no-till planted to corn, with the planter set up to plant the seeds in a narrow slot, minimizing soil disturbance. Hairy vetch that was not killed by the planting operation was mown. Interesting differences between the CONV and LIP-1 cropping systems were noted in nitrate nitrogen levels in the soil throughout the growing season (Figures 18-5 and 18-6) and among the tillage regimes within each cropping system.

The LIP-2 rotation was planted with wheat and soybeans in 1989. Wheat yields ranged from 43 to 23 bu/acre, and soybean yields ranged from 28 to 21 bu/acre, with the higher yields being in the moldboard plow tillage regimes and the lowest being in the no-till system (Table 18-8). Expenses are minimized in this system because no herbicides are used and the soybeans are drilled into the established grain crop. However, the high cost of harvesting both crops and the relatively low yield of soybeans in 1989 compared with the soybean yield in the CONV system in 1988 indicate that for the moldboard plow, chisel/disk, and ridge-till systems, monocultures of soybeans are more profitable, while in the no-till system the LIP relay crop is more profitable than the CONV monoculture crop (Wes Musser, Agricultural Economics Department, The Pennsylvania State University, University Park, personal communication of preliminary results, 1990).

More time is needed to determine whether the yields in the reduced-tillage plots go up over time relative to those in the moldboard plow regime. Reports in the literature indicate that 10 years or more is sometimes needed before no-till systems come to equilibrium. The value of the conversion experiment was not fully appreciated until after the fourth and fifth growing seasons, and it is anticipated that this trial will also increase in value, in terms of information generated, over time. It has already provided a useful comparison of energy use in LIP versus CONV cropping systems by using various tillage regimes for 2 years, and the comparison will be more representative after 4 and 8 years of data are collected (the second and third rotation cycles). Shifts in weed populations and abundance can be examined and long-term economic performance assessed as the trial matures.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 18-5 Soil nitrate nitrogen levels in the conventional cropping system (30 lbs/acre starter and 100 lbs/acre sidedress nitrogen applied as ammonium nitrate) for the (A) 0- to 2-inch and (B) 2- to 8-inch soil layers in the low-input, reduced-tillage cropping system experiment, Rodale Research Center, 1989.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 18-6 Soil nitrate nitrogen levels in the low-input (LIP-1) cropping system (nitrogen from hairy vetch cover crop) for the (A) 0- to 2-inch and (B) 2- to 8-inch soil layers in the low-input, reduced-tillage cropping system experiment, Rodale Research Center, 1989.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 18-8 Wheat Yield, Soybean Yield, and Weed Biomass in the Low-Input, Reduced-Tillage Experiment, Rodale Research Center, 1989

Treatment (LIP-2)

Wheat Yield (bu/acre)

Soybean Yield (bu/acre)

Weed Biomass (lbs/acre)

Plow

43a*

28a

330bcde

Chisel

33b

28a

599bc

Ridge till

30b

24ab

668b

No-till

23c

21b

490bcd

NOTE: LIP, low input.

* Duncan's multiple range test was performed by analysis of variance using Statistical Analysis System software; comparisons are within columns.

LONG-TERM CROPPING SYSTEMS COMPARISONS

In addition to the three experiments highlighted in this chapter, several other experiments with similar objectives have begun or are being initiated at various locations around the country. Recently, a working conference was held at the Rodale Research Center (in preparation) to bring together researchers working on long-term cropping systems studies, to discuss common concerns, and to search for ways to strengthen existing collaborations and develop new working relationships among the various institutions represented. Ongoing trials represented at the conference (besides those at the Rodale Research Center and Cornell University) were those at Michigan State University (East Lansing), the University of Georgia (Athens), North Dakota State University (Fargo) (Gardner, 1989), Ohio State University (Columbus) (Edwards and Creamer 1989), North Carolina State University (Raleigh) (King 1990), and Clemson University (Clemson, South Carolina). Trials are also ongoing at the University of Nebraska (Lincoln) (Helmers et al., 1986; Sahs and Lesoing, 1985,), South Dakota State University (Brookings), and the University of California (Davis). Experiments are in the planning stages or are about to be initiated at Rutgers University (New Brunswick, New Jersey), the University of Wisconsin (Madison), the University of Minnesota (St. Paul) (Crookston and Nelson, 1989), and possibly other locations as well. All these trials have the common theme of a long-term planning horizon, and each is looking for LIP sustainable cropping systems as alternatives to the CONV systems for their region. Some trials include a tillage component as well as different levels and different types of inputs; in addition, they compare various crop rotations. Several experiments have been conducted to examine the crop rotation effect and

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

the effect of using animal manure over a long period of time (e.g., Lazarus et al. [1980], Odell et al. [1974], Smith [1942]; see also the summary by Brown [1989]), but an evaluation of LIP alternatives was not an explicit objective of these trials.

All researchers and institutions share the common problem of obtaining secure funding sources with a 5- to 10-year (or longer) planning horizon. With the exception of funding for long-term ecological research sites from the National Science Foundation, other funding sources, sometimes including experiment station commitment, tend to run on a year-to-year time frame. A national agricultural funding commitment to long-term research, such as USDA-funded long-term ecological research sites, is needed if these experiments are to continue. Most of these experiments are in their first or second cropping season, with the exception of those at the University of Nebraska (1990, year 15), Rodale Research Center (1990, year 10), and North Carolina State University (1990, year 5). Valuable data have been and continue to be collected at two or more sites simultaneously, that is, soil microbial studies at the University of Nebraska and Rodale Research Center (Fraser, 1984), 15N studies at Michigan State University and the Rodale Research Center (Harris et al., 1989), and organic matter studies at Ohio State University and the Rodale Research Center (M. Wander, Ohio State University, Columbus, personal communication), generally through the participation of graduate students. As more long-term experiments are initiated, the opportunities for collaboration among researchers at several sites that represent various climatic zones increase, and the chances for truly understanding the mechanisms important for pest control and nutrient cycling are enhanced.

MEANINGFUL INTEGRATION OF FARMER AND RESEARCHER INFORMATION

Many of the sustainable agriculture programs at various locations around the country are also linked to networks of farmers who advise researchers on the direction of on-station research and who function as research collaborators by conducting experiments and demonstration trials on their farms. Researchers involved with the cropping systems experiment at Cornell University currently conduct research on reduced-tillage techniques, cover crop overseeding, reduced herbicide use through banded applications, cultivation for weed control, and manure management with six New York State farmers (Mt. Pleasant, 1990). At the Rodale Research Center, members of the agronomy department serve as technical advisers to the Midwest on-farm research network (McNamara and Janke, 1988; McNamara et al., 1987) and also work with local farmers in southeastern Pennsylvania who are exploring overseeding options, crop rotation diversification, soybean relay cropping (Peters, 1989), and no-till planting into cover crops.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

Some farmers are able to articulate the successes of their farming practices to researcher and farmer audiences without the benefit of a structured network to disseminate the results (Kirschenmann, 1988; Thompson and Thompson, 1989), but even well-known spokespeople such as the Thompsons benefit from their affiliation with networks of other farmer-researchers, such as the Rodale Institute Network and the Practical Farmers of Iowa. Networks facilitate information dissemination by organizing and publicizing field days and farm tours and by organizing panels of farmers to speak at events cosponsored by the Cooperative Extension Service. Networks of farmer-researchers also facilitate information flow back to researchers as to what works (e.g., hairy vetch is great for nitrogen production and soil improvement), what does not work (e.g., no-till planting into incompletely killed rye grain), the fine-tuning of systems that is needed (e.g., do not fertilize wheat when you are relay cropping soybeans), and the next set of questions that need to be addressed (e.g., why do my soil phosphorus and potassium levels seem to be going up in fields with cover crops, even without manure or mineral fertilizer additions?). Farmer-directed on-farm research empowers farmers because it encourages them to answer their own questions (Janke and McNamara, 1988; Janke et al., 1990) as they go through the transition period. It allows them to cut back on chemical and fertilizer inputs gradually, testing the results at each step. Many of the farmers in the Rodale Institute Network compare their usual rate of nitrogen fertilizer application with a reduced rate. The Practical Farmers of Iowa have been comparing low versus high nitrogen application rates and mechanical cultivation versus herbicide use for corn and soybean production in ridge-tillage systems (Practical Farmers of Iowa Newsletter, 1989).

Limitations of on-farm research include the difficulty of doing extensive sampling (this is easier to accomplish at research station sites) and the amount of time required by the farmer to conduct complex, long-term trials. On-farm trials of 2 or 3 years or similar 1-year trials repeated for 2 or more consecutive years are more feasible. Workable designs include two or three treatments replicated four to six times. There remains a role, however, for testing of farmer and researcher questions in complex, long-term systems trials at research stations. On-farm research complements, but does not replace, work done at research stations.

SUMMARY

The support of long-term cropping systems research from 1988 to the present by the LISA program of USDA is to be applauded. However, long-term experiments require secure funding sources to attract the necessary intellectual talent and commitment of researchers and other field station personnel. Farmers serve a valuable role as advisers to those conducting

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

studies at research stations and as collaborators who find some answers but who also raise many questions and generate valuable hypotheses that need to be tested in long-term, replicated trials.

One example includes use of the Rodale conversion experiment to test the commonly held belief that yields go down during the first 3 to 5 years after the withdrawal of chemical inputs from the cropping system. The cause of the lower yields was thought to be related to changes in biological processes in the soil. The Rodale trial has shown that yields were, in fact, lower in the LIP systems compared with those in the CONV system for the first 4 years, but only for corn. The yield suppression was found to be largely due to the low levels of nitrogen available to the crop, a situation that changed in year 5, once legumes were in the rotation for at least two cycles. Soil biology appeared to play a role in the amount and timing of nitrogen availability in both types of LIP rotations, and greater microbial activity and soil fauna populations were found in the LIP plots compared with those in the CONV plots. Studies are under way to explore the role of the labile fraction of soil organic matter in nutrient bioavailability in these systems.

The second experiment described in this chapter was also designed to answer questions generated by farmers. In New York State, farmers believe that cool soils limit corn silage production and that no-till farming will not work for them. The Cornell trial tests the reduced-tillage technique of ridge tillage in a long-term cropping systems context. Ridge tillage is a technique that leaves the crop residue on the field for the duration of the winter and spring (protecting the field from soil erosion) and that requires no primary tillage before crops are planted in the spring (energy savings); the well-drained ridges warm up faster than do the cool wet soils. These farmers also feel locked in to growing corn several years in a row on their best land while they use their other land for pastures and woodlots. Crop diversification does not seem to be a viable option, but the Cornell trial is demonstrating the benefits of red clover and ryegrass overseeding to improve tilth and help suppress weeds in what would otherwise have been a strictly monoculture situation.

The third trial tests a technique that was tried on farms long before research stations had the nerve to attempt it—that is, no-till cropping systems without herbicides. Farmers in a number of midwestern states have been experimenting with rye and hairy vetch, and some were even beginning to plant soybeans by the no-till method into rye with some success. The LIP reduced tillage experiment at Rodale is attempting to combine information from farmers about reduced tillage, including chisel/disk-based systems, ridge-tillage, and especially no-till (mow-sow) planting into cover crops, with what researchers have learned from the conversion experiment about how to grow crops without purchased fertilizers or pesticides (diver-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

sified crop rotations that include legumes). This long-term cropping systems trial is, possibly, the only site in the country where not only are tillage regimes in similar cropping systems being compared but where two of the three cropping systems in the experiment are LIP (no-pesticide) systems.

Once the experiment has gone through one or two rotation cycles (4 to 8 years) and the tillage systems are well established, this trial will be a valuable testing ground for hypotheses regarding soil organic matter, soil biology, and plant-animal-soil-microbe interactions. In addition, this will be a site where agronomic questions can be answered about system feasibility, and energy and economic comparisons can be calculated from a realistic, multiyear data set.

ACKNOWLEDGMENTS

The authors express their gratitude to Richard Harwood, William Liebhardt, and Martin Culik, who began the farming systems trial at the Rodale Research Center. The authors continue to benefit from their foresight in planning and implementing this trial.

The authors also acknowledge the various funding sources that have made this research possible, including the LISA program of USDA, the Charles Stewart Mott Foundation, the Pennsylvania Energy Development Authority, the Cornell Agricultural Experiment Station and Rodale Press.

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Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Thompson, D., and S. Thompson. 1989. The 1989 Report. Boone, Iowa. Mimeograph.

U.S. Department of Agriculture. 1980. Report and Recommendations on Organic Farming. Washington, D.C.: U.S. Department of Agriculture.

Vargas, A. M., R. R. Janke, W. N. Musser, D. K Israel, M. D. Shaw, J. M. Hamlett, S. E. Peters, and F. Higdon. 1989. Comparison of Energy Use in Conventional

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

and Low-Input Reduced Tillage Cropping Systems. Staff Paper No. 169. University Park, Pa.: Agricultural Economics and Rural Sociology Department, The Pennsylvania State University.

Waltman, W. J., and T. W. Scott. 1989. Soils of the Rodale Research Farm. Kutztown, Pa.: Rodale Research Center. Mimeograph.

Werner, M. R. 1988. Impact of Conversion to Organic Agricultural Practices on Soil Invertebrate Ecosystems. Ph.D. dissertation. College of Environmental Science and Forestry, State University of New York, Syracuse.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

19

Perspectives for Sustainable Agriculture from Plant Nutrient Management Experiences in Pennsylvania

Les E. Lanyon

Research and education in plant nutrient management have a long history in Pennsylvania. More than 90 percent of the cash receipts for field crops and animals on Pennsylvania farms result from the sale of animal products (Pennsylvania Agricultural Statistics Service, 1989). This emphasis on livestock in the state's agriculture has encouraged the production of a range of crops, usually on the farms where the animals are located. Forage production has been a major enterprise on the many ruminant-based farms. However, present trends are for a decreased emphasis on production of the complete ration on the farm and increased reliance on off-farm sources of feeds, especially feed concentrates. McSweeny and Jenkins (1989) reported that, on average, approximately 50 percent of the rations for dairy cows in Pennsylvania was purchased feed. At the extreme end of the feed supply spectrum, a trend has developed, primarily with nonruminant animals, for 100 percent of the feed to be provided by off-farm sources. Whether the feed is produced on the farm or purchased, manure is generated that must be distributed away from the livestock facilities.

The production of forages, especially forage legumes, and the requirements for manure handling have created the foundations for nutrient management in Pennsylvania. Although the idea of nutrient management on farms in Pennsylvania has extensive historic roots, the goals and challenges of nutrient management have not remained the same with time.

Historically, low inputs of plant nutrient-containing materials, such as purchased feeds or fertilizers, necessitated the use of internal farm nutrient sources and the organization of many farm activities to deal with this oligotrophy. With the changes in off-farm sources of nutrients following World

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

War II, especially nitrogen fertilizers and the availability of off-farm feeds, the emphasis on efficient use of internal nutrient sources diminished in the face of net farm nutrient loading. In this process of nutrient loading, deficiencies of plant nutrients in the soil and on the farm were eliminated; and the nutrient factors that limit crop production shifted from the amount of nutrients available to utilization of the host of on- and off-farm sources. In recent times, the reported use of fertilizer plant nutrients in Pennsylvania has actually decreased to only 80 percent of the 1955 levels (Berry and Hargett, 1987). This change in fertilizer use reflects in part the transformation of Pennsylvania farms from nutrient-poor to nutrient-rich status.

The linkage of animal numbers on particular farms, and by association, the amount of manure produced, to the potential nutrients that could be applied to crops was significantly diminished following World War II by the ready availability of off-farm feeds and the technology used to house large numbers of animals in high-density facilities. The shift in emphasis for manure management went from the use of an essential nutrient source to the least direct cost distribution of manure. The costs of distribution are not exclusively economic, but they could include a host of on-farm factors related to the practice.

The least direct cost distribution of manure continues to be an effective foundation for nutrient management strategies on many farms in Pennsylvania. In some cases, however, the external effects of manure management practices on the most eutrophic farms could be substantial when nutrients are discharged into the environment. Therefore, current approaches to nutrient management must focus on procedures for supplying nutrients in a timely fashion and at rates that are appropriate for the crop and soil conditions, but perhaps not by the least direct cost method. The most eutrophic farms must transfer manure away from the farm to comply with the nutrient utilization potential of the farm where manure is generated.

As farm conditions have changed, the role of the immediate community around the farm has changed from being a primary market and the source of limited inputs to being a stopover point in the process of long-distance market and input supply transportation. The surrounding community is currently concerned with the impacts of farm operations on the environment. An as yet undefined community must be developed in the future to cooperate with the farms to distribute manure within an acceptable area. This possible future cooperation will involve the geographic area where manure will be applied and the information on which to base the appropriate transfer of nutrients, if not direct financial support to do so. This new community will likely be made up of different people and a different geographic region from the one that is the source of the farm inputs and the one in which the products of the farm are distributed.

In one part of the nutrient management research and extension program

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

in Pennsylvania, the emphasis has been to understand nutrient management strategy implications for crop and livestock farms, to relate the strategies to environmental and economic performance indicators, and to formulate and support a whole-farm nutrient management process with the appropriate tools. Field studies of complete farm operations are under way to monitor the actual dynamics of nutrients in nutrient management pathways on Pennsylvania farms and to develop techniques for on-farm nutrient management. The goals are to recognize and understand the site specificity (specific characteristics of the farm site) and information richness (wealth of available information about the farms). These goals are similar to those of sustainable agriculture.

In Pennsylvania, the experience of dealing with whole farms, especially those that focus on livestock production, has been a source of insight into the science of agricultural research and education. It is the inspiration for a review of normal science approaches to research and for the need to work cooperatively with farmers in the context of a complex, interconnected, biological managed system.

PLANT NUTRIENT MANAGEMENT STRATEGY IMPLICATIONS

Westphal et al. (1989) investigated the consequences of several strategies for dealing with manure nitrogen (N) utilization, residual legume N, and manure application approaches on a simulated dairy farm. Each of these was evaluated by assuming either that the available N supply was limited to that which could be used by the crop or that the available N could be oversupplied. In the first case, the N was managed so that groundwater contamination by leaching excess N beyond the plant root zone was avoided. In the second case, the risk of N contamination of groundwater was much greater because of the potential for applications in excess of the potential amounts that could be used by plants. Crop sequences of 2 years of corn (C) followed by 3 years of alfalfa (A) (C-C-A-A-A) or 3 years of corn preceding 3 years of alfalfa (C-C-C-A-A-A) were considered.

The combination of the best agronomic recommendation (a high efficiency of manure N utilization and the full amount of residual N available from the preceding alfalfa crop) and the best environmental protection criterion (the amount of N supplied was restricted to that required by the crop) resulted in the lowest economic net return to the farm when compared with other less efficient or sensitive strategies ( Table 19-1). The potential N utilization by the crops was the factor that restricted the amount of manure that could potentially be spread and thus restricted the number of cows on the farm. Since each 1,400-pound (lb) dairy cow produces approximately 21 tons of manure containing almost 210 lbs of total N (Midwest Plan Service, 1975) per year, from 42 to 110 lbs of N available from the

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 19-1 Relationship of Crop Sequence and Nutrient Management Strategies to Herd Size and Net Return on a Simulated 125-Acre Dairy Farm in Pennsylvania

Crop Sequence

Manure N Efficiency

Available N Restriction

Herd Size (Number)

Limiting Factor

Net Return*

C-C-A-A-A

Low

Yes

72

Feed

99

 

Low

No

72

Feed

99

 

High

Yes

41

Crop N use

23

 

High

No

72

Feed

100 ($36,838)

C-C-C-A-A-A

Low

Yes

84

Feed

98

 

Low

No

84

Feed

98

 

High

Yes

69

Crop N use

79

 

High

No

84

Feed

100 ($44,347)

NOTE: N, nitrogen; C, corn; A, alfalfa.

* Percentage of maximum return within a crop sequence (dollar amount of maximum return is given in parentheses).

Original simulation used for comparison within a crop sequence.

SOURCE: P. J. Westphal, L. E. Lanyon, and E. J. Partenheimer. 1989.Plant nutrient management strategy implications for optimal herdsize performance of a simulated dairy farm. Agricultural Systems31:381–394.

total must be used in crop production for each cow that is added to the herd. The net return to the farm operation was reduced much less when the percentage of corn in the crop sequence was increased from 40 to 50 percent. About 25 percent more land was available for manure application, and higher amounts of manure could be applied to the corn since there was an additional year beyond the influence of the residual N from the alfalfa in the C-C-C-A-A-A crop sequence.

Application of manure to alfalfa in the last year of the crop sequence resulted in an increased number of cows on the farm for those strategies in which herd size was limited by the potential area where manure could be applied (Table 19-2). Inclusion of the off-farm purchase of grain for lactating dairy cows increased the net economic returns to the farm (Table 19-3). When the requirement that phosphorus (P) and potassium (K) application to the soil and utilization by the plants be balanced (constant maintenance by testing levels in soil) was relaxed, the numbers of cows and net returns again increased. Therefore, two practices that provided relatively little positive contribution to the crops, manure application to alfalfa and increases in the levels of P and K in soil (above the sufficiency level), resulted in the enhanced economic performance of the simulated dairy farm.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 19-2 Herd Size and Net Return to a Simulated 125-Acre Dairy Farm with and without Manure Applied to Alfalfa in the Last Year of Two Crop Sequences

Crop Sequence

Manure N Efficiency

Available N Restriction

Manure on Alfalfa

Herd Size (Number)

Limiting Factor

Net Return*

C-C-A-A-A

High

Yes

No

41

Crop N use

100 ($8,429)

 

High

Yes

Yes

60

Crop N use

352

C-C-C-A-A-A

High

Yes

No

69

Crop N use

100 ($35,213)

 

High

Yes

Yes

84

Crop N use

126

NOTE: N, nitrogen; C. corn: A, alfalfa.

* Percentage of net return with no manure application to alfalfa within a crop sequence (dollar amount of net return is given in parentheses).

Original simulation used for comparison within a crop sequence.

SOURCE: P. J. Westphal, L. E. Lanyon, and E. J. Partenheimer. 1989.Plant nutrient management strategy implications for optimal herdsize performance of a simulated dairy farm. Agricultural Systems31:381–394.

TABLE 19-3 Herd Size and Net Return to a Simulated 125-Acre Dairy Farm as Influenced by Corn Grain Purchases and Restrictions on Soil Test Phosphorus and Potassium Levels for Two Crop Sequences

Corn Grain Purchase

Manure N Efficiency

Restrictions Available N

Soil Tests

Number of Cows

Limiting Factor

Net Return*

No

Low

Yes

Yes

84

Feed

100 ($43,337)

Yes

Low

Yes

Yes

94

Crop P use

114

Yes

Low

Yes

No

105

Crop N use

122

Yes

Low

No

No

135

Manure application

150

No

High

No

Yes

84

Feed

100 ($44,347)

Yes

High

No

No

135

Manure application

148

NOTE: N, nitrogen: P. phosphorus.

* Percentage net return within an available N restriction group (dollar amount of net return is given in parentheses).

Original simulation used for comparison within an available N restriction group.

A practical manure application limit of 50 tons/acre was imposed.

SOURCE: P. J. Westphal, L. E. Lanyon, and E. J. Partenheimer. 1989.Plant nutrient management strategy implications for optimal herdsize performance of a simulated dairy farm. Agricultural Systems31:381–394.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

The enhanced performance was most notable when outcomes were compared with base scenarios in which the nutrients were managed in an efficient and environmentally sensitive manner.

The energy economy of a dairy farm can be affected substantially by a variety of nutrient management strategies such as incorporation of manure into soil or application of manure to the soil surface and crop sequence selection (Vinten-Johansen et al., 1990). However, the significance of the practices can be influenced by other features of the crop production system such as tillage practices (no-till or conventional tillage, for example), the frequency and power requirements of the machinery operations, and machinery size. In a whole-farm linear program simulation, incorporation of manure into soil increased the fuel requirements slightly in all situations compared with those for surface application, but it significantly reduced the energy input to the farm embodied in fertilizer (Table 19-4). A reduction of tillage (no-till) for corn production had a greater energy conservation effect than did N conservation by manure incorporation when a C-C-A-A-A legume-based rotation was considered. When a forage legume in combination with corn rather than corn monoculture was used, the total energy requirements were reduced substantially through a reduction in the indirect energy embodied in fertilizer and pesticides. Nevertheless, the direct energy (fuel) consumption for the crop sequence with the forage crop increased as a result of the greater fuel requirements for forage crop production. The cultural practices for these crops require more trips across each field in a growing season than does corn production. A transition from monoculture corn to a mixed set of crops requiring different machines and field and management operations also has additional requirements for the farm that must be considered beyond the energy performance criteria of the nutrient management practices.

MONITORING WHOLE FARMS

Unlike the relatively straightforward flow of materials on cash crop farms, the complex internal cycles of the flow of managed materials on crop and livestock farms are not readily adapted to accurate monitoring. Bacon et al. (1990) described an approach for measuring the flows of nutrients within a hierarchically nested set of management units on a Pennsylvania dairy farm. The essential elements of the approach were an effective recordkeeping system based on data collected by the farmer, with sampling and data management provided by the research team. Internal flows of crops and manure were routed across a 25-ton-capacity mechanical scale, and samples were collected for nutrient concentration determinations. Material flow at the farm gate was determined from farm financial records, and input suppliers were interviewed to identify the geographic sources of many materials.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 19-4 Selectcd Energy and Production System Inputs for a Simulated 125-Acre Dairy Farm with Different Crop Sequences, Tillage Methods, and Manure either Injected into the Soil or Surface Applied

 

Continuous Corn Crop Sequence

C-C-A-A-A Crop Sequence

 

No-Till

 

Conventional Till

 

No-Till

 

Conventional Till

 

Input

Injected Manure

Surface Manure

Injected Manure

Surface Manure

Injected Manure

Surface Manure

Injected Manure

Surface Manure

Energy (dfe)*

Fuel

787

771

1,251

1,235

1,224

1,203

1,402

1,394

Fertilizer

2,229

2,603

2,229

2,603

220

330

220

330

Pesticides

429

429

286

286

264

264

209

209

Machinery

870

870

1,387

1,387

1,348

1,348

1,348

1,348

Purchased feeds

1,497

1,497

1,497

1,497

1,172

1,040

1,172

1,172

Miscellaneous

748

721

737

765

969

1,123

1,178

1,178

Total

6,560

6,891

7,387

7,773

5,197

5,197

5,529

5,631

Energy product−1 (dfe cwt−1)

0.82

0.86

0.92

0.97

0.65

0.66

0.69

0.70

Crop production

Corn grain (acres)

11.9

11.9

11.9

11.9

32.8

32.8

32.8

32.8

Corn silage (acres)

111.6

111.6

111.6

111.6

16.5

16.5

16.5

16.5

Alfalfa (acres)

0

0

0

0

74.1

74.1

74.1

74.1

Fuel (gallons)

787

771

1,251

1,235

1,224

1,203

1,402

1,394

Nitrogen (lbs)

14,046

17,023

14,046

17,023

1,204

2,037

1,169

1,958

Herbicides (lbs)

639

639

463

463

381

381

311

311

NOTE: C, corn; A, alfalfa.

* Diesel fuel equivalent (42.9 Mcal/gallon).

Diesel fuel equivalent per hundred weight of milk.

SOURCE: C. J. Vinten-Johansen, L. E. Lanyon, and K. Q. Stephenson.1990. Reducing external inputs to a simulated small dairy farm. Agriculture,Ecosystems and Environment 31:225–242.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

This approach to studying a farm was preferred to the description of a representative farm operation. First, because work was done on an actual farm, the real problems and conditions encountered by farmers were sure to become apparent. The monitoring program could then evolve to address these real problems. Because much of the information concerning the principles for utilizing a variety of on- and off-farm nutrient sources is well established, the on-farm work could provide insight into possible barriers to the implementation of this existing information. Second, the attempt to study a whole system implied that the integrity of the actual connections among the various parts of the system, the surroundings, and the manager would be maintained. These connections are just as critical to the definition of a whole system as are the components of the system. Finally, the tools developed to study simulated representative farms, while appropriate for such analyses, are not as well suited for application to specific farms. The site specificity and information richness of individual farms can overwhelm representative models. Part of the goal of studying an actual farm was to develop techniques that might be transferred to specific farms and to integrate the research results into appropriate tools for application at the individual farm level.

Even though the animal density on the farm was relatively high (approximately 1.1 animal units/acre; an example of an animal unit is a 1,000-lb dairy cow), the managed flow of nutrients to and from the fields was relatively well balanced (Table 19-5). Balance in the fields was achieved through crop management, resulting in high crop yields; through the application of manure on rented ground, even though it was planted to alfalfa; and through judicious purchases of fertilizer. The importance of animals to the whole farm nutrient flow was apparent in the primary nutrient loading of the farm from animal feed rather than from fertilizer purchased for crop production (Table 19-6). The set of crop and animal factors contributing to the management of on- and off-farm plant nutrient sources reflects the site-specific management by the farmer in both enterprise areas and the potential productivity of the soils. A simple description of the animal-to-land-area ratio was not adequate to characterize the nutrient balance status of the farm fields or the nutrient flow on the whole farm.

Site specificity is readily recognized as part of the internal structure and function of a system, but the surroundings of a farm create site-specific relationships as well. The study farm was located in an intensive agricultural area with an abundance of input suppliers that were supported by many input sources. The suppliers of inputs to the farm identified local, regional, and even international sources of materials that contributed to the nutrient loading of the farm. Many of the regional geographic sources of farm material inputs are identified on the map in Figure 19-1.

A linear program simulation of this same dairy farm compared costs

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 19-5 Nutrient Balance of the Managed Flows Classified by Material or Source for all the Fields on a Pennsylvania Dairy Farm in 1985 and 1986

 

1985

1986

Input or Output

TN

AN

P

K

TN

AN

P

K

Input (lbs/yr)

Fertilizer

900

900

977

514

2,335

2,335

785

0

Manure

19,847

6,099

4,086

16,015

16,429

4,269

3,076

16,948

Residual

377

377

686

686

Fixation*

7,918

7,918

6,447

6,447

Total

29,042

15,658

5,063

16,529

25,898

13,737

3,861

16,948

Crop output (lbs/yr)

20,414

20,414

3,195

17,856

20,460

20,460

3,312

16,052

Nutrient balance (lbs/yr)

8,628

−4,756

1,868

−1,327

5,438

−6,723

549

896

Nutrient balance (lbs/acre/yr)

90

−49

20

−13

56

−70

5

9

NOTE: TN, total nitrogen; AN, available nitrogen; P, phosphorus; K, potassium. Available nutrient balance (inputs minus outputs) was calculated with the total nutrient outputs.

* Assuming 60 percent of the alfalfa herbage nitrogen content is from fixation.

SOURCE: S. C. Bacon, L. E. Lanyon, and R. M. Schlauder, Jr. 1990.Plant nutrient flow in the managed pathways of an intensive dairyfarm. Agronomy Journal 82:755–761.

TABLE 19-6 Nutrient Balance of the Managed Flows in 1985 and 1986 for a Pennsylvania Dairy Farm

 

1985

1986

Input or Output

N

P

K

N

P

K

Input (lbs/yr)

Fertilizer

900

977

514

2,335

785

0

Feed

12,758

2,412

3,283

9,100

1,118

2,531

Bedding

926

126

895

75

11

163

Total

14,584

3,515

4,692

11,510

1,914

2,694

Output (lbs/yr)

Livestock

406

95

24

150

35

9

Product

5,656

942

1,321

5,532

922

1,290

Manure

646

287

919

0

0

0

Total

6,708

1,323

2,264

5,682

957

1,299

Nutrient balance (lbs/yr)

7,876

2,192

2,428

5,828

957

1,395

NOTE: N, nitrogen; P, phosphorus; K, potassium. Nutrient balance is inputs minus outputs.

SOURCE: S. C. Bacon, L. E. Lanyon. and R. M. Schlauder. Jr. 1990.Plant nutrient flow in the managed pathways of an intensive dairyfarm. Agronomy Journal 82:755–761.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 19-1 Geographic relationships of a southeastern Pennsylvania dairy farm and the sources of selected production inputs and the outlets for farm products.

associated with a material flow monitoring program that involvedweighing of farm materials and several material sampling and analysis intensities (Lemberg, 1989). These operational parameters of the monitoring program were considered within the context of common property or open-access water resources perspectives (Runge, 1981). Under conditions of common property, all parts of society control the use and pollution of water re-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

sources, but under open access there are no constraints on individual behavior in relationship to the resource.

The net returns to the farm with the monitoring program in place were not significantly less than the returns in a comparable simulation without a monitoring program, except that there was no labor or analysis cost for the same information collected in the program. In both cases, the net returns were greater than those in the simulation in which manure was disposed of on the land and the complete plant nutrient requirements were provided by fertilizers. In contrast, the water resource relationship perspective of society had a considerable effect on the potential farm profitability when the amounts of nutrients applied were limited strictly to those required by the crops. These restrictions resulted in manure that was produced but unspread under the common property perspective compared with the openaccess perspective. The complex and indivisible ratio of nutrients in the manure compared with the crop requirements precluded the use of manure and favored the application of fertilizers that contained the necessary nutrients in exact proportions.

In general, the method for monitoring farm material inputs and, consequently, on-farm nutrient utilization appears to be economically feasible. On the other hand, societal perspectives for acceptable management may deserve more attention. A consensus on the appropriate precision and range of performances that define responsible management may be very critical to the potential utilization of organic sources of plant nutrients on crop and livestock farms.

PLANT NUTRIENT MANAGEMENT PROCESS

The difficulties in predicting the best management practices from general principles of crop nutrient supply and the need to deal with site specificity are being integrated into a nutrient management process in Pennsylvania (Figure 19-2). The stages of this process parallel those of tactical planning, day-to-day plan implementation, and control operations that have been used widely in business administration (Meredith and Gibbs, 1984).

This management process has several distinctive features. First, it approaches a farm at the farmer's tactical decision-making level. With this level of resolution for the human activity system (Checkland, 1981), it is a potentially viable heuristic for participation with the farmer. The usual facts about, for example, nutrient requirements of crops and the dynamics of N volatilization, are embedded in the process, but these facts do not constitute the entire process, nor do these facts determine the strategy within which the process operates. This approach to management facilitates the implementation of a particular nutrient management strategy, but it does not determine the strategy. The technical expert does not need to know

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 19-2 Proposed nutrient management process to integrate management advisers with the farmer in on-farm management activities. Source: L. E. Lanyon and D. B. Beegle. 1989. The role of on-farm nutrient balance assessments in an integrated approach to nutrient management. Journal of Soil and Water Conservation 44:164–168.

the nutrient management answer for a specific farm before becominginvolved in the process.

Second, the management process is iterative. That is, the process does not need to achieve the right answer on the first attempt. The opportunity exists to monitor the system, to respond to performance indicators, and to

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

innovate based on the specifics of the system functions. This openness to iteration is a mechanism by which existing practice can be integrated into the process. Because farmers create the farm based on their own particular rationales, the likely path of action on a particular farm is most closely related to the action of the preceding year rather than to some completely new selection from a wide spectrum of possibilities. The opportunity to incorporate the history of the farm explicitly may be an effective bridge between old and new management systems.

Third, new tools must be developed to support the various stages of the process. These tools are a means to link the technical experts with the operation of the farm and to complement the management skills of the farmer. The ultimate goal of the process is to enhance the manager's understanding of the farm operation so that goals can be incorporated into the operation of the farm based on farm managers ' knowledge of their operations rather than, simply, the requirements of good practices.

Computer-based tools have been developed to complement the management activities in several parts of the management process in the nutrient management research and education effort in Pennsylvania (Lanyon and Beegle, 1989). Planning tools are available that estimate manure production and that allocate the manure to fields based on the nutrient requirements of the crops (Beegle and Durst, 1989). A program has been developed to collect information about actual farm operations and to process that information (Lanyon and Meij, 1989). The information can be submitted directly to the farm manager or can be the basis of implementation assessment activities (Lanyon and Schlauder, 1988).

Further refinement of existing tools, the development of tools to complement the remaining parts of the process, and implementation of the process by personnel or institutions are still needed. Selected tools have been accepted and used in the field, but the integrated approach has not yet been accepted.

NORMAL SCIENCE, LEARNING, AND PROFESSIONAL ACTIVITIES

The outcomes of normal science, like puzzle solving (Kuhn, 1970), can be embedded within the proposed management process, but normal science is unlikely to coopt the process. The puzzle-solving metaphor implies that the ruling paradigm is known and that a missing piece can be discovered. Nutrient management, on the other hand, incorporates site specificity and information richness, that is, the particular elements of place and management. It does not address the missing pieces of a management system. For normal science to deal with site specificity and information richness, thin chains of logic (hypotheses) must be developed with as many factorial

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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treatment combinations as are needed, and experimental measurements must be made to test (disprove) the hypotheses. Farmers faced with nutrient management decisions are more likely to encounter a complex web of interconnections rather than a thin chain with a weak link to be stressed until it breaks. Farmers do not have the flexibility to wait until all possible hypotheses have been tested before they make each management decision.

Modern science suggests that the surroundings or experimental conditions also influence the outcomes of the experiments themselves. The measurements cannot be separated from the experiment or the surroundings. Consequently, even complete factorial experiments that must hold all other factors constant may be inadequate to address the much different condition of site specificity on an actual farm. Other factors may be relevant, to an unknown degree, to the efficacy of the experimental results in the setting outside the experiment. Nevertheless, these experiments should not be abandoned, as they contribute to the formulation of universal principles, but their limitations should be recognized when the focus of the effort is the particular and concrete elements of site specificity and information richness.

Modern science also recognizes the impact of surroundings on the characteristics of internal system structure and function, as emphasized in irreversible thermodynamics. This revision of the traditional reversible thermodynamic perspective has transformed the focus from the singularity of ideal reversible phenomena to the multiplicity of real irreversible phenomena (Nicolis and Prigogine, 1989). Irreversible phenomena can follow multiple paths in the transformation of a given state, such as a change in pressure and volume of a unit of gas, compared with the single reversible path. Irreversible transformations affect and are affected by the surroundings, while reversible transformations are unaffected by the surroundings. The irreversibility of a process leads to the requirement for an infinite amount of information to predict the behavior of a dynamic system with multiple potential paths. This situation is often described as the sensitivity of a system to initial conditions. It is known, however, that an infinite amount of information for predicting the behavior of particular real systems is not attainable. Therefore, approaches to dealing with the possibilities of these systems that are outside the domain of traditional science must be considered.

Contemporary cognitive theories recognize the elementary left brain/ right brain orientations of fact-based/art-based humans (Hampden-Turner, 1981) or the less simplistic paradigm that views the mind as a process shaped by individual physiology and a unique set of personal experiences (Minsky, 1986). Farmers who participate in the management process possess a certain perspective and certain abilities, that is, distinctive cognitive styles. Each style affects the selection of management strategies, the effi-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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cacy of implementation activities, and the acceptability of system performance. Thus, the additional site specificity and information richness of the manager must be included in an approach to complex (i.e., real-world) systems such as farms.

The proposal of a formal management process may not be compatible with the cognitive styles of all members of the farming population. However, it can be a common framework by which to approach both farms and farmers. With some effort, it could be adapted to a variety of management styles by sensitive buffering between the managers of the technical process and the farm managers. The incentive for farmer participation in such a process may be the feasibility of performance-based rather than specification-based farming. The establishment by farmers, at an acceptable level of confidence, of farming methods for their own farms may be a practical, more satisfying approach to management than farming according to a prescription from off-farm experts.

Many people may be more comfortable with compromise or satisfactory situations than scientists who, in their professional lives, strive for the black and white results of hypothesis testing. Off-farm experts generally deal best with judgments about static and unchanging physical objects. Generally, experts perform poorly in situations in which dynamic systems that are linked to human behavior are confronted (Shanteau, 1989). Farms and farmers, especially those focusing on site specificity and information richness, are more likely to be dynamic and complex.

Chambers (1983) further emphasizes that professionals tend to be inculcated with values and preferences during their education that influence the projects, clientele, and locations they select for future work. He advocates a willingness on the part of the professionals to deal with the last as well as the first of these preferences and to assume new roles as the outsiders. The professionals in these new roles do not emphasize the transfer of technology, but attempt to empower farmers to learn, adapt, and do better (Chambers, 1989).

This brief overview of modern science, contemporary cognitive theories, and an alternative approach for practicing professionals suggests that the activities of professional agriculturalists be crafted within these evolving contexts. The harnessing of ever more powerful computers to achieve mechanistic solutions of natural system relationships based on normal science will not adequately incorporate these new perspectives. Ulanowicz (1986) contends that in a phenomenological perspective of complex ecological systems, such as the operation of a specific farm, one is less concerned with true and false than with degrees of adequacy of process description. This perspective may be the basis for a contemporary paradigm by which to understand particular farms with their site specificity and information richness.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Focusing instead on an integrative management process could facilitate a mode of learning about farms for farmers, professionals, and perhaps even society. Such a process will be enhanced with ongoing application. Its conceptualization and implementation may serve to integrate universal principles that are developed in the course of normal science with the “messiness” that characterizes real systems. The approaches of normal science and management of information about the world and the people in it are quite different, but they can be complementary and synergistic.

CONCLUSION

An approach to farm systems that is sensitive to the contributions of normal science and the opportunities of an integrative management process will be able to take advantage of both science and management alternatives. The site specificity and information richness that are essential in contemporary plant nutrient management also have been heralded as the hallmarks of sustainable agriculture. Therefore, the utility of normal science in addressing issues of sustainability may be as limited as it is for nutrient management. There are no missing pieces in the existing landscape of the world in which sustainable agriculture must make its place. Sustainability is a complex strategy, not a fact that can be experimentally measured or perhaps even defined. Sustainability as a strategy is a guide for real-world operations. It depends on a value decision of what is right or wrong. Facts about nature and the world do not answer value questions (Gould, 1982).

Normal science may be inadequate as the source of sustainable agriculture. Likewise, by itself, a site-specific, information-rich management process cannot ensure that a sustainable agriculture system will be implemented. The evolution of real systems depends too much on the surroundings to be specified simply by understandings of or intentions for the system. For sustainability to become a guiding principle of agriculture, it must become a widespread and consistent strategy reflected in informed management actions and reinforced by society. Anthropologist R. A. Rappaport (1979) emphasizes that detailed knowledge alone cannot replace the human expression of respect as the critical element in our relationship with the environment.

REFERENCES

Bacon, S. C., L. E. Lanyon, and R. M. Schlauder, Jr. 1990. Plant nutrient flow in the managed pathways of an intensive dairy farm. Agronomy Journal 82:755–761.

Beegle, D. B., and P. T. Durst. 1989. Farm Nutrient Management Worksheet. Version 2.01, ECS AAG-0103 v2.01. University Park, Pa.: Department of Agronomy, The Pennsylvania State University.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Berry, J. T., and N. L. Hargett. 1987. 1986 Fertilizer Summary Data. Bulletin No. Y-197. Muscle Shoals, Ala.: National Fertilizer Development Center, Tennessee Valley Authority.

Chambers, R. 1983. Rural Development. New York: Longman Inc.

Chambers, R. 1989. Reversals, institutions and change. Pp. 181–195 in Farmer First, Intermediate Technology Publications, R. Chambers, A. Pacey, and L. A. Thrupp, eds. New York: The Bootstrap Press.

Checkland, P. 1981. Systems Thinking, Systems Practice Chichester, England: John Wiley & Sons.

Gould, S. J. 1982. Non-moral nature. Natural History >91(2):19–26.

Hampden-Turner, C. 1981. Maps of the Mind. New York: Macmillan.

Kuhn, T. S. 1970. The Structure of Scientific Revolutions, 2nd ed. Chicago: The University of Chicago Press.

Lanyon, L. E., and D. B. Beegle. 1989. The role of on-farm nutrient balance assessments in an integrated approach to nutrient management. Journal of Soil and Water Conservation 44:164–168.

Lanyon, L. E., and H. K. Meij. 1989. FINFO: Field and Farm Technical Information Management Program—Users Guide. Agronomy Series No. 106. University Park, Pa.: Department of Agronomy, The Pennsylvania State University.

Lanyon, L. E., and R. M. Schlauder, Jr. 1988. Nutrient Management Assessment Worksheets. Version 2.0L. Agronomy Series No. 103. University Park, Pa.: Department of Agronomy, The Pennsylvania State University.

Lemberg, B. 1989. An Economic Evaluation of a Method to Obtain Farm-Specific Nutrient Information on a Lancaster County Dairy Farm Under Two Nutrient Management Strategies. M.S. thesis, Department of Agricultural Economics and Rural Sociology, The Pennsylvania State University, University Park, Pa.

McSweeny, W. T., and L. C. Jenkins. 1989. 1988 Pennsylvania Dairy Farm Business Summary. Extension Circular 374. University Park, Pa.: College of Agriculture, The Pennsylvania State University.

Meredith, J. R., and T. E. Gibbs. 1984. The Management of Operations, 2nd ed. New York: John Wiley & Sons.

Midwest Plan Service. 1975. Livestock Water Facilities Handbook MWPS-18. Ames, Iowa: Midwest Plan Service, Iowa State University.

Minsky, M. 1986. The Society of Mind. New York: Simon & Schuster.

Nicolis, G., and I. Prigogine. 1989. Exploring Complexity. New York: W. H. Freeman.

Pennsylvania Agricultural Statistics Service. 1989. Statistical Summary 1988–89. Harrisburg, Pa.: Pennsylvania Agricultural Statistics Service.

Rappaport, R. A. 1979. Ecology, Meaning, and Religion. Berkeley, Calif.: North Atlantic Books.

Runge, C. F. 1981. Common property externalities: Isolation, assurance, and resource depletion in a traditional grazing context. American Journal of Agricultural Economics63:595–606.

Shanteau, J. 1989. Psychological characteristics of agricultural experts: Application to expert systems.Pp. 163–179 in Proceedings of Climate and Agriculture Systems Approaches to Decision Making, A. Weiss, ed. Washington, D.C.: American Meteorological Society.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Ulanowicz, R. E. 1989. Growth and Development. New York: Springer-Verlag.

Vinten-Johansen, C. J., L. E. Lanyon, and K. Q. Stephenson. 1990. Reducing external inputs to a simulated small diary farm.Agriculture, Ecosystems and Environment31:225–242.

Westphal, P. J., L. E. Lanyon, and E. J. Partenheimer. 1989. Plant nutrient management strategy implications for optimal herd size performance of a simulated dairy farm. Agricultural Systems31:381–394.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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20

Use of Fungal Pathogens for Biological Control of Insect Pests

Raymond I. Carruthers, Alan J. Sawyer, and Kirsten Hural

Although the vast majority of insects are either beneficial or harmless to humans, control of a few pest species has been a challenge since the beginning of time. Actually, fewer than 1 percent of known insect species are considered pests (Davidson and Lyon, 1979). These insects destroy crops, damage dwellings, eat food from the table, and even attack people. In response to these pests and their insults, some of the most lethal toxins known have been developed and spread throughout the environment. Although they are effective in the short term, chemical pesticides are expensive and typically provide only temporary relief, as the explosive reproductive and evolutionary capacities of the insects allow them to develop mechanisms of resistance to these and other control strategies (Metcalf, 1980).

Secondary effects (human health hazards, damage to nontarget organisms, environmental pollution, etc.) produced by the application of pesticides to residential and agricultural lands for control of insects, plant diseases, and weeds suggest that some of these control strategies have become self-defeating (Perkins, 1982). Clearly, however, chemical pesticides are valuable tools that must be used wisely to combat insect pests. The challenge, then, is to use them only when necessary and in consort with other more ecological methods of pest control. In response to this need, the discipline of integrated pest management (IPM) (Allen, 1980) has evolved a philosophy of controlling pest species based on intimate knowledge of pest population dynamics and associations with the surrounding ecosystem. Multiple tactics, including chemical, cultural, and biological methods, are used collectively with respect for the environment, to maintain pest numbers below economically significant levels (Allen, 1980; Hoy and Herzog, 1985).

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Biological control, which is the use of natural enemies to help regulate pest populations, has been the mainstay of many IPM programs. In most cases, biological control involves the use of parasites, predators, or pathogens that attack, injure, or kill the target pest. To that end, the U.S. Department of Agriculture (USDA) has been involved in the development and implementation of biological control programs for insect and weed pests for over 100 years (Coppel and Mertins, 1977; King and Coulson, 1988). Most of these efforts have focused on the collection and use of exotic parasites and predators for control of insect pests. Several classical examples of biological control successes have been documented by Huffaker (1974) and Coppel and Mertins (1977). Although some early attempts were made to use insect pathogens as biological control agents, much less emphasis has been placed on microbial control than on other areas of biological control. Recently, more emphasis has been placed on the use of insect pathogens (bacteria, viruses, and fungi) as biological control agents. These pathogens are known to produce widespread epizootics in nature, often decimating their insect host populations, but scientists have been relatively unsuccessful in producing insect disease outbreaks at will (Carruthers and Soper, 1987). Most research efforts have focused on the isolation, development, and production of highly pathogenic microbes with characteristics favoring long-term storage and application, as if they were chemical insecticides. Although this approach has been successful with some bacteria, the use of microbes as replacements for chemical insecticides has usually resulted in unpredictable and inadequate responses under field conditions (Fuxa, 1987). One of the primary reasons for these failures is the lack of understanding of the natural dynamics of host-pathogen life systems. Diseases develop in complex ways based on biological and physical associations between the host, the pathogen, and the environment. Understanding of these associations in general and more specifically on a system-by-system basis should provide a significant amount of assistance in the ability to manipulate insect pathogens for IPM purposes.

Fungal pathogens are important natural biological control agents of many insects and other arthropods and frequently cause epizootics that significantly reduce host populations (Burges, 1981; Carruthers and Soper, 1987; MacLeod, 1963; McCoy et al., 1988). Because of the frequency of natural epizootics and the conspicuous symptoms associated with fungus-induced mortality (McCoy et al., 1988; Steinhaus, 1963), the significance of fungi in regulating insect populations was noted early in recorded history by the ancient Chinese (Roberts and Humber, 1981). In fact, Beauveria bassiana. an insect-pathogenic fungus, was the first microbe recognized as a pathogen and was used by Agostino Bassi (1835) to demonstrate his germ theory of disease.

Approximately 750 species of entomopathogenic fungi are known from

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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85 genera (exclusive of the 115 genera in the order Laboulbeniales) found throughout the classes of fungi (Gillespie and Moorhouse, 1989; McCoy et al., 1988; Roberts and Humber, 1981). The majority of the entomopathogenic species are classified in the classes Hyphomycetes, Zygomycetes (order Entomophthorales), and Ascomycetes (in particular, the genera Cordyceps and Torubiella). These pathogens cause mycoses in many different taxa of arthropods and in almost every order of the Insecta (Bell, 1974; Gillespie and Moorhouse, 1989). They are known to infect all life stages of insects and are commonly found in aquatic, terrestrial, and subterranean habitats (Ferron, 1978). Although fungal pathogens have much in common with viruses, bacteria, and other insect-pathogenic microbes, they are unique in many ways (Ferron, 1978). Perhaps the most significant difference lies in the mode of infection; whereas most entomopathogens infect their hosts through the gut following consumption, fungi typically penetrate the insect cuticle and thus are the only major pathogens known to infect insects with sucking mouthparts, orders Hemiptera and Homoptera (Roberts and Humber, 1981).

Attempts to manipulate fungi as biological control agents of insects began in the late nineteenth century with only poor to moderate success (Krassilistchik, 1888; Metchnikoff, 1879; Snow, 1895; Steinhaus, 1956). Little basic or applied research was conducted on entomopathogenic fungi from the late nineteenth century until the late 1960s, when interest in the use of fungi as biological control agents increased because of problems with chemical control (Roberts, 1979). Although several successful programs have been developed over the past 20 years (Burges, 1981; Ferron, 1978; Gillespie and Moorhouse, 1989), very few fungi have been used extensively for biological control of insect pests. The reasons for this are numerous, but a general lack of understanding of fungal population biology and the environmental factors that limit disease development have certainly restricted their use (Allen et al., 1978; Carruthers and Soper, 1987; McCoy et al., 1988).

Naturally occurring epizootics caused by fungal pathogens, particularly those caused by fungi in the order Entomophthorales, are noted frequently in both natural and managed ecosystems (Carruthers and Soper, 1987; Carruthers et al., 1985b; McCoy et al., 1988; Mohamed et al., 1977; Nordin et al., 1983; Pickford and Riegert, 1964; Soper et al., 1976; Wilding, 1975, 1981). Because of the catastrophic impacts these pathogens have on their host populations, they hold significant potential for biological control of some pest species (Carruthers and Soper, 1987; Ferron, 1978; McCoy, 1981; Wilding, 1981). Definite limitations on their manipulation as biological control agents exist, and some researchers feel that fungus-induced epizootics are too dependent on high host densities and environmental conditions, particularly moisture (Bucher, 1964). The majority of researchers who

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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study insect pathogens, however, believe that fungi will play a vital role in IPM systems in the near future (Allen et al., 1978; Carruthers and Soper, 1987; Fuxa, 1987; McCoy et al., 1988).

This chapter discusses naturally occurring fungal diseases, basic host and pathogen biology, disease development and spread, environmental factors that allow or restrict disease progression, and the application of fungal pathogens in specific biological control situations. This is not meant to be an exhaustive review but, rather, an overview of the subject. Readers interested in more comprehensive reviews on fungal pathology in general or on specific taxa of fungal pathogens are referred to Steinhaus (1963), Burges and Hussey (1971), Burges (1981) and McCoy et al., (1988). Those interested in additional information on epizootiology, biological control, and use of fungi in IPM should refer to Tanada (1963), Ferron (1978), Wilding (1981), Carruthers and Soper (1987), Fuxa (1987), and McCoy et al. (1988).

FUNGAL PATHOGEN LIFE CYCLES AND BIOLOGY

Despite the taxonomic diversity of entomopathogenic fungi, there are many similarities among the major groups in their basic life histories and ecology. In general, the pathogen life cycle begins with spore germination and penetration of the host's cuticle, followed by a rapid proliferation of fungal cells which ultimately results in the death of the host. Host death may be followed by the production of infective spores which can immediately repeat the cycle, or by the production of resting spores or other resistant structures which require a period of dormancy.

Infective spores of entomopathogenic fungi may be asexual propagules such as conidia of the order Entomophthorales and the class Deuteromycetes, or they may be the result of sexual recombination such as the ascospores of the genus Hypocrella (the class Ascomycetes) (Evans, 1982) or the biflagellate zygote of the genus Coelomomyces (Chytridiomycetes) (Whisler et al., 1975b). After contact with a potential host, infective spores adhere to the insect cuticle if host recognition is positive (Al-Aidroos and Roberts, 1978). Adhesive processes have not yet been intensively studied in entomogenous fungi; however, both physical and chemical interactions are probably important (Fargues, 1984). Epicuticular compounds such as fatty acids, amino acids, and glucosamines are thought to play a significant role in determining the specificity and pathogenicity of entomopathogenic fungi (Boucias and Pendland, 1984; Kerwin, 1983; Saito and Aoki, 1983; Smith and Grula, 1982; Woods and Grula, 1984).

Spore germination is highly dependent on moisture and probably requires free water (Kramer, 1980; Newman and Carner, 1975; Roberts and Campbell, 1977; Shimazu, 1977), but this requirement may be met by moisture conditions of the microclimate in the absence of measurable precipi-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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tation (Ben-Zev and Kenneth, 1980; Hall and Dunn, 1957; Kramer, 1980; Mullens et al., 1987; Tanada, 1963). Penetration of the cuticle is accomplished by the germ tube itself or by the formation of an appressorium which attaches to the cuticle and gives rise to a narrow penetration peg (Boucias and Pendland, 1982; Roberts and Humber, 1981; Wraight et al., in press a; Zacharuk, 1973). Penetration is both a mechanical and an enzymatic process (Charnley, 1984; McCoy et al., 1988; St. Leger et al., 1987, 1988b).

Vegetative growth in the insect hemocoel is common to most entomopathogenic fungi (Roberts and Humber, 1981) and usually consists of discrete yeastlike structures or hyphal bodies. This form of growth, in contrast to the typical filamentous fungal mycelium, allows the entomopathogen to disperse rapidly and colonize the insect's circulatory system and increases the fungal surface area which is in contact with the nutrient medium. Several species of the order Entomophthorales produce vegetative protoplasts (cells without cell walls) within the hemocoel (Butt et al., 1981; Large et al., 1988; Nolan, 1985; Tyrrel and MacLeod, 1972) which may help the pathogen to escape detection by the host's immune responses. The length of the incubation period varies among species; however, disease development during the vegetative stage is typically temperature dependent (Carruthers and Soper, 1987; Carruthers et al., 1985a; Hall, 1981). Fungi have been observed to elicit insect immune responses, but it is not known what role they may play in preventing or slowing the development of mycoses (Butt et al., 1988; Gupta, 1986; St. Leger et al., 1988a).

Pathogens may simply overcome their hosts by consumption of the available nutrients in the hemocoel, as do most lower fungi such as the genera Coelomomyces and Lagenidium and most genera of the order Entomophthorales (Roberts, 1981) or by digestion of host tissues and organs (Brobyn and Wilding, 1977). In cases in which fungi overcome their hosts after a relatively short period of vegetative growth, toxins produced by the pathogen are presumed to be the cause of death (Roberts, 1981). Compounds toxic to insects are produced by several entomopathogenic fungi both in vitro and in vivo (Roberts, 1981). However, their role in pathogen-induced mortality in nature is not well understood.

Shortly after host death, the fungal hyphae penetrate the host cuticle from within and terminate in the formation of sporophores (usually conidiophores) that yield asexual spores (conidia) which function as dispersive and infective units. In many species of fungi, the production of conidia is highly dependent on moisture (Millstein et al., 1983; Wilding, 1969). Conidia are the infective propagules of secondary infection and determine disease development and spread within a season. Environmental factors that control conidial production, survival, and germination are critical to the rate of epizootic development (Carruthers and Soper, 1987).

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Entomopathogenic fungi survive adverse environmental conditions or the absence of their host by producing resting spores or other resistant structures, or they survive as dormant mycelia in dried insect mummies (Kenneth et al., 1972; Wilding, 1973). Most species of the order Entomophthorales produce a spherical, thick-walled resting spore (MacLeod, 1963) which may also be the sexual stage of these fungi (McCabe et al., 1984). The conditions required to break the dormancy of resting spores are not well understood (Wilding, 1981), although temperature, moisture, and photoperiod have been indicated as triggers in some species (Perry and Latge, 1982; Wallace et al., 1976). When dormancy requirements have been met and other environmental conditions are correct, resting spores germinate and produce germ conidia which then initiate mycoses in susceptible hosts. Some species of the order Entomophthorales such as Pandora neoaphidis apparently do not produce resting spores (Milner et al., 1983) and presumably overwinter as dormant mycelia inside mummified insects. Fungi in the classes Ascomycetes and Deuteromycetes may produce specialized masses of hardened vegetative tissue called sclerotia or stromata, as in the genera Cordyceps and Torubiella, or modified hyphae called chlamydospores, as in the genera Beauveria and Metarhizium (McCoy et al., 1988; Roberts and Humber, 1981).

Many variations of this basic life cycle occur in different species of entomopathogenic fungi. A unique feature within the order Entomophthorales, for example, is the active discharge of infective conidia and their ability to produce repetitional conidia in the absence of a suitable host (King and Humber, 1981). Primary conidia of Zoophthora radicans, a common entomophthoralean pathogen, can give rise to actively discharged secondary conidia, which in turn may produce tertiary conidia and so on until the protoplastic reserves of the spore have been consumed. Alternatively, they may produce capilloconidia, which are passively detached conidia borne atop elongate capillary conidiophores. Capilloconidia have a sticky substance at one end and are positioned at an angle which is thought to enable them to be picked up by insects walking over a surface (McCoy et al., 1988; Soper, 1985). The type of spore produced is dependent on host availability and environmental conditions during germination. Another variation on the basic theme is the heteroecious cycle or alternate hosts as in Coelomomyces infections of mosquitoes and copepods. A biflagellate zygote, a fusion product of gametes produced in the copepod alternate host, infects mosquito larvae by encysting on the cuticle (Zebold et al., 1979). Following infection, hyphae proliferate throughout the hemocoel and fat body, ultimately producing thick-walled multinucleate sporangia at their tips. Upon death of the larvae, sporangia are released into the water. Meiosis occurs prior to sporangial germination and results in the production of haploid meiospores which are capable of infecting copepod hosts. Each

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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meiospore forms a gametophyte within the copepod and matures into a gametangium which releases gametes of a single mating type. The fusion of opposite mating types completes the cycle by producing mosquito-infective biflagellate zygotes (Federici, 1981; Whisler et al., 1975b).

DISEASE EPIZOOTIOLOGY

Natural disease development and spread are governed by characteristics of both host and pathogen populations and by the environment in which their interactions occur. In managed ecosystems this scheme is further complicated as human intervention adds a fourth component. These four components (host, pathogen, environment, and humans) and their interactions have been represented by the disease tetrahedron (Carruthers and Soper, 1987; Zadoks and Schein, 1979). The factors encompassed by this model are necessarily interrelated, and although they may be discussed individually, it must remembered that their interactions are critical to overall system behavior.

The Pathogen Population

Properties of the pathogen population that are important in epizootiology include virulence and pathogenicity, dispersal and survival in the host's environment, and inoculum density and spatial distribution (Tanada and Fuxa, 1987).

Virulence refers to the intensity of the disease caused by a pathogen, whereas pathogenicity refers to an organism's ability to cause disease. Most fungal pathogens are considered highly virulent relative to other pathogenic organisms because they typically have short incubation periods, produce copious amounts of secondary inoculum, and can cause a rapid increase in disease prevalence. A fungal species which is pathogenic on a wide range of hosts may be more likely to persist in an environment because of the availability of alternate hosts. With a greater number of susceptible hosts, there may be a greater reservoir of inoculum available to produce an epizootic (Tanada, 1963).

There are many reports of intraspecific variation in virulence among strains of a pathogen (Daoust and Roberts, 1982; Ignoffo and Garcia, 1985; Papierok and Wilding, 1981). Very often the isolates compared in these studies were collected from locations in different parts of the world. In order to understand the role of intraspecific variability with respect to virulence, it is necessary to measure the extent of variation in well-defined populations of hosts and pathogens. To our knowledge, no studies of this type have yet been published.

Pathogen survival in the host's environment is necessary for the long-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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term persistence of disease in the population; as previously mentioned, fungi accomplish this by producing various types of resting spores or structures. The ability to survive adverse conditions or periods of host absence may determine the frequency with which epizootics occur, because without some means of survival, infection is dependent upon the movement of inoculum into the host's habitat (Tanada, 1963). Some pathogens, such as Beauveria bassiana and Metarhizium anisopliae, are ubiquitous and cause mycoses frequently, suggesting that they have successfully persisted in the host's environment. A possible advantage of naturally occurring pathogens over microbial insecticides may be their ability to persist over long periods of time.

Dispersal is necessary for the rapid spread of disease. Abiotic factors such as rain or wind may carry spores, or the movement of infected and uninfected hosts may transport inoculum from one place to another (Hall and Dunn, 1957). Some fungal pathogens cause their hosts to climb to aerial locations just prior to death (MacLeod, 1963); such behavior may aid dispersal of infective conidia which may rain down on or blow to nearby hosts.

Pathogen population density and spatial distribution are key factors in the development of an epizootic, as they affect the likelihood of contact with viable hosts (Tanada and Fuxa, 1987). There has been substantial work on the relationship between pathogen dose and mortality in the laboratory, generally concluding that mortality increases with inoculum dose (Pinnock and Brand, 1981). Although this relationship has rarely been studied under realistic conditions, studies of Entomophaga grylli infection of the clear-winged grasshopper revealed that field infection reasonably followed a logistic response curve (see below and Figure 20-1).

The Host Population

Important host population factors which must be considered are susceptibility, density, movement, and spatial distribution of individuals. There are very few reports of genetic variabilities in the susceptibilities of insects to fungal disease in natural populations. Paperiok and Wilding (1979) reported that one of two clones of the pea aphid ( Acyrthosiphon pisum) was resistant to infection by Conidiobolus obscurus compared with the other highly susceptible clone. Milner (1982, 1985) was able to characterize field-derived clones of pea aphids as resistant or susceptible based on percent mortality when exposed to a particular isolate of Pandora neoaphidis. Undoubtedly, the population dynamics of variability in host resistance and pathogen virulence would have an impact on epizootiology and the long-term stability of disease incidence in the population: however, this is another area of research which lacks sufficient study.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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FIGURE 20-1 Entomophaga grylli doses (conidia per 0.5-square-meter cage) producing different levels of infection under field conditions.

Although climatic conditions may be limiting for disease development, under nonlimiting conditions, host density may directly influence the rate of disease buildup (Benz, 1987; Carruthers et al., 1985b; Watanabe, 1987). In some situations the spatial arrangement of hosts may be more important than the actual numbers of individuals. If hosts are highly aggregated, it may be difficult for the pathogen to disperse between aggregates, unless infected hosts or pathogen propagules are highly mobile.

The Abiotic Environment

Abiotic environmental factors such as moisture, temperature, and solar radiation affect many of the biotic factors mentioned above; moreover, they may determine whether or not infection can occur. Atmospheric moisture is often considered the most important abiotic factor in the epizootiology of fungal diseases (Fuxa and Tanada, 1987; Nordin et al., 1983). As mentioned in the previous section, germination and sporulation of most fungi are highly dependent on moisture. However, fungi are able to acquire

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

moisture from sources other than precipitation, such as dew or from the boundary layer of the host. The humidity of the microclimate, such as a dense plant canopy, may be much higher than that of the ambient air (Fuxa and Tanada, 1987; Kramer, 1980; Tanada, 1963).

Temperature-dependent processes that directly affect the progression of disease are the rate at which insects develop, the rate of fungal development within the insect, and the rate and quantity of spore production (Benz, 1987). Most fungal pathogens do well at all temperatures suitable for insect growth. The effects of temperature and humidity are intimately related: Some fungi may tolerate higher temperatures if there is more moisture in the air, as condensation may readily occur and water loss is minimized (Benz, 1987).

Conidia may be very sensitive to solar radiation (Carruthers et al., 1988a; Ignoffo et al., 1977), and spore longevity and germination may be improved if the microhabitat, such as a dense crop canopy, can protect the conidia from direct radiation (Figure 20-2).

Secondary infection, that is host-to-host infection, is crucial in the epizootiology of fungal diseases, in that repetitive cycles of infection result in a rapid increase in disease prevalence (Zadoks and Schein, 1979). Pathogens that have many secondary cycles during one or a few generations of the host are most likely to cause dramatic epizootics. Transmission efficiency has been shown theoretically to be an important parameter related to the rate at which secondary infections occur and thus of epizootic progress (Anderson and May, 1980). Transmission of fungal pathogens occurs primarily through the insect integument; this may be accomplished through direct host-to-host contact or by host contact with infective spores in the environment, such as conidia deposited on plant surfaces. Disease transmission is thus influenced by host and inoculum density and spatial distribution. Theoretical models have demonstrated that a pathogen can be maintained within a host population only if the host density exceeds a threshold value, and this value has been defined as being inversely proportional to transmission efficiency (Anderson and May, 1980). Brown and Nordin (1982) determined that the threshold density for Zoophthora spp. epizootics of alfalfa weevil populations is 1.7 weevils per stem. Subsequent field studies showed that larval densities below this threshold could not support a Zoophthora epizootic. Nordin et al. (1983) concluded that the initiation of disease was best correlated with degree-day accumulations, and that epizootic dynamics were controlled by atmospheric moisture levels, as long as the host population remained above the threshold density. Further methods of enhancing the development and spread of Zoophthora spp. are discussed in a subsequent section.

In recent years, systems analysis and modeling have been recognized as useful aids to understanding the complex dynamics of fungal epizootics

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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FIGURE 20-2 Proportion germination of Entomophaga grylli conidia (p) as predicted by cumulative solar radiation (∫Ldt) by the exponential decay model, p = 0.5582bi(∫Ldt) (estimates of bi for each canopy area are provided below). Results from different canopy locations are shown both in a composite group for easy comparison and individually with the corresponding observed data (A, bottom of dense canopy, b = −0.237: B, middle of dense canopy, b = −1.228: C, top of dense canopy and bottom of open canopy, b = −1.915; D. middle and top of open canopy, b = −3.804). Source: R. I. Carruthers, Z. Feng. M. E. Ramos, and R. S. Soper. 1988. The effect of solar radiation on the survival of Entomophaga grylli conidia. Journal of Invertebrate Path ology 52:154.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

(Anderson and May, 1980; Brown, 1987; Carruthers, 1985; Carruthers and Soper, 1987; Carruthers et al., 1988b; Onstad and Carruthers, 1990). Relatively simple models have been used to explore basic questions in epizootiology (Anderson, 1982; Anderson and May, 1980; Brown, 1984; Brown and Nordin, 1982; Hochberg, 1989; Regniere, 1984). More detailed simulation models of specific host-pathogen systems have also been developed for a few fungal pathogens (Carruthers et al., 1986, 1988b). These models and the techniques of systems science have proven to be very useful in guiding the collection, analysis, and synthesis of information about the dynamics of host and pathogen life systems. In addition to providing basic understanding, models can assist in pest management decision making and can be used to help design and evaluate strategies for employing fungal pathogens in biological control programs. Expert systems (Logan, 1988) and intelligent modeling systems (Larkin and Carruthers, 1990; Larkin et al., 1988) are becoming available to make the analytical power of systems techniques more accessible to scientists and pest management specialists who may have little experience with modeling.

Although epizootics of fungal disease are known to cause major declines in pest populations, very little information is available on the long-term regulatory ability of these pathogens. This is particularly true during periods of enzootic activity, when disease prevalence is low and signs of host infection are difficult to detect. Disease assessment is complicated further if pathogen-induced mortality occurs in habitats that are difficult to observe, as is the case in soil or aquatic ecosystems. Over the past two decades, however, several significant descriptive and experimental studies on disease dynamics have provided new insights into the population biology and possible use of fungi as biological control agents (Carruthers et al., 1985b; Kish and Allen, 1978; MacLeod et al., 1966; Nordin et al., 1983; Soper and MacLeod, 1981; Soper et al., 1976). As it is not possible to review all the significant literature, some relevant examples have been chosen to highlight the impact of fungal pathogens on their hosts, both in natural and managed ecosystems.

COWORKERS AND COOPERATORS INVOLVED IN SPECIFIC RESEARCH PROJECTS

The Plant Protection Research Unit, Agricultural Research Service (ARS), USDA, has been involved in the development and use of fungal pathogens of insects in several different ecosystems, including forest, rangeland, and agricultural production systems. Cooperators are listed in Table 20-1, along with their involvement in specific projects, as indicated in the footnotes. Implementation projects have involved cooperators from action agencies, such as state departments of agriculture and markets, The U.S. Forest Ser-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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vice and the Animal and Plant Health Inspection Service (APHIS) of USDA, and cooperating ranchers and farmers in areas where actual field projects have been conducted.

TABLE 20-1 Research Team Members Involved in Development and Use of Fungal Pathogens

Affiliation and Team Member

Affiliation and Team Member

USDA-ARS

Cornell University

R. I. Carruthers*#

Z. Feng.||

H. Firstencel||.#

S. Galaini-Wraight.#

R. A. Humber*.||.||

K. Hural*.||.#

A. J. Sawyer||.#

T. S. Larkin||

R. S. Soper*..||.||.#

D.G. Robson.||

USDA-APHIS

Boyce Thompson Institute for Plant Research

R. N. Foster||

M.E. Ramos||.||

J. L. Fowler||

D. W. Roberts..#

S. P. Wraight#

Illinois Natural History Survey

 

J. V. Maddox#

 

S. Roberts#

 

NOTE: USDA, U.S. Department of Agriculture; ARS, Agricultural Research Service; APHIS, Animal and Plant Health Inspection Service.

* Population genetics of the aphid pathogen Pandora neoaphidis.

Microbial control of the Colorado potato beetle using Beauveria bassiana.

Microbial control of the European corn borer using Beauveria bassiana.

|| Evaluation of Entomophaga grylli-like biological control agents for grasshopper management.

|| Introduction of Entomophaga maimaiga for gypsy moth biological control.

# Introduction of Zoopthora radicans for biological control of leafhoppers.

SPECIFIC EXAMPLES OF INSECT BIOLOGICAL CONTROL RESEARCH USING FUNGAL PATHOGENS

The use of entomopathogenic fungi for biological control in managed ecosystems has followed four basic strategies: (1) awareness of natural biological control impacts, (2) augmentation of natural enemies, (3) enhancement of impacts through active manipulations, and (4) introduction of exotic natural enemies (Ignoffo, 1985; McCoy et al., 1988). Examples of ongoing research that demonstrate the important aspects of and the levels

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

of expertise that investigators have in each of these areas of biological control are provided. The first example comes from an on-going research project aimed at developing a basic understanding of natural host-pathogen dynamics in a rangeland ecosystem. This project has evolved into an active biological control project that is now aimed at introducing fungal pathogens (both native and exotic germ plasm) into areas where they do not currently exist.

Awareness of Naturally Occurring Pathogens and Their Relevance to Biocontrol
Entomophaga grylli Mycosis of Grasshoppers

Rangelands are low-energy ecological systems that provide resources to people primarily in the form of forage for grazing livestock. Although rangelands are low in productivity per unit area, their vastness (ca. 1.0 billion acres in the continental United States [Heath et al. 1973], which is the equivalent of five times the area of Texas) makes them extremely important in terms of food production and general resource management. Grasshoppers are the dominant group of herbivorous insect pests associated with rangelands worldwide. Their populations have plagued humans from the earliest days of recorded history, and they continue to do so today. In the United States alone, millions of federal dollars have been spent on grasshopper spray programs each year over the past decade, and populations are still expected to increase. In other areas of the world, grasshoppers and migratory locusts are commonly seen in outbreak numbers year after year.

In response to this pest problem, the ARS of USDA has initiated a variety of research programs to study grasshopper biology and management. One of these projects is focused on the development of grasshopper pathogens as long-term biological control agents. One such pathogen is Entomophaga grylli, a fungus that attacks several grasshopper species (Carruthers and Soper, 1987). This pathogen has caused widespread but sporadic epidemics in grasshopper populations and has been responsible for major population reductions of several economically important pest species. Although this pathogen is known to play a significant role in the regulation of natural grasshopper populations, very little was known about its ecological associations with different grasshopper hosts or with other components of the environment. Interest in manipulating this pathogen for use in IPM programs was the stimulus for initiating a long-term research project on the natural dynamics of E. grylli (Carruthers and Soper, 1987; Carruthers et al., 1988a, in press). For the past few years, descriptive and experimental studies have been conducted that are designed to determine key abiotic and biotic factors involved in regulating disease dynamics under natural field conditions.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

E. grylli is an obligate fungal pathogen of grasshoppers and thus is nonpathogenic to humans, beneficial insects, and other nontarget organisms. Study of its parasitic and free-living stages is important in understanding its biology and interactions with grasshopper hosts. E. grylli has a complex life cycle. Resting spores overwinter in the soil and germinate each spring. The phenology of germination depends on local environmental conditions. Upon the breaking of dormancy, resting spores produce specialized spores (germ conidia) that are forcibly ejected from the soil into the lower plant canopy where they contact grasshoppers, produce germ tubes, and then penetrate the body wall of the insect through enzymatic and mechanical actions. Once it is inside the insect, the pathogen multiplies rapidly while digesting away the surrounding host tissues. Under normal field conditions, this disease retards egg laying and feeding damage prior to actual host death, which occurs approximately 7 to 10 days after initial exposure. Upon host death, the fungus produces either resting spores, which are released into the soil to initiate infection in subsequent years, or airborne conidia, which either germinate immediately (within 24 hours) or die from adverse environmental conditions.

Although each dead grasshopper may be the source of several million fungal conidia, these free-living spores are extremely ephemeral, as their survival is highly influenced by temperature, moisture, and solar radiation (Figure 20-2). To maximize their infection potential, E. grylli induces grasshopper mortality in midafternoon, followed by conidial production starting in the early evening. This synchronizes maximum spore production with dew formation and minimum solar radiation, conditions that increase the chance of germination and infection. The magnitude of host infection is directly related to the inoculum level (Figure 20-1) and microenvironmental conditions in the habitat where infection occurs (Feng et al., in press). If conidia are successful in contacting a susceptible host under appropriate environmental conditions, secondary infection (infection initiated from spores produced within the same season) will perpetuate the disease through another cycle. Since the incubation period of this disease is substantially shorter than the life cycle of the grasshoppers (Carruthers et al., in press), the pathogen may have several generations each season, with the exact number of cycles depending on environmental conditions. Natural epizootics of this disease commonly produce high levels of grasshopper mortality (Figure 20-3) and have been known to reduce outbreak populations of grasshoppers to nondamaging levels (Riegert, 1968). Based on research conducted on the natural dynamics of this pathogen in restricted ecosystems and detailed laboratory evaluations of important pathobiological characteristics, APHIS and ARS of USDA are now cooperating on a biological control implementation program by using E. grylli for the control of rangeland grasshoppers in North Dakota and

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

FIGURE 20-3 Grasshopper population density over a 4-year period and levels of Entomophaga grylli mycosis. Grasshopper mortality caused by this pathogen was clearly responsible for the observed population declines.

Alaska. If successful, this program is likely to expand into adjacent range-land areas.

Augmentation of Fungal Pathogens for Biological Control

Augmentation (increasing pathogen inoculum density) through the development of microbial insecticides has received substantial attention and is discussed here only briefly, as it is the focus of other articles (Burges, 1981; Burges and Hussey, 1971; McCoy, 1990). It must be said, however, that augmentation has not only taken the form of microbials applied like pesticides with the goal of high acute host mortality but has also been used to initiate epizootics prematurely (Ferron, 1981; Ignoffo et al., 1976) or in situations in which epizootics would not develop naturally (McCoy, 1981; Riba, 1984). In these cases, disease development is dependent not only on the efficacy of the fungal material originally applied to the target host but also on the pathogen's ability to become established in the environment and produce a secondary inoculum that is capable of polycyclic infection. These methods of pathogen augmentation require detailed information about host, pathogen, and disease dynamics that have been researched only recently (Allen et al., 1978; Carruthers and Soper, 1987; McCoy et al., 1988).

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Beauveria bassiana Mycosis of Colorado Potato Beetles

The fungal pathogen Beauveria bassiana was investigated as a potential mycoinsecticide for control of the Colorado potato beetle, Leptinotarsa decemilineata. Increased resistance of this pest to various chemical insecticides and groundwater pollution associated with chemical use prompted investigations into the use of fungi as an alternative means of control. Soviet researchers (Lappa, 1978) found specific isolates of B. bassiana to be effective in controlling populations of the Colorado potato beetle in the Soviet Union. Based on their strategies, field trials were first conducted in potato-growing regions of Long Island, New York (Galaini, 1984), using spore preparations developed by Abbott Laboratories. Many difficulties were encountered in the initial stages of this project, including extremely high Colorado potato beetle populations, low efficacy of the fungal propagules, and improper application strategies. Over the course of 3 years of investigation, several improvements in the use of B. bassiana as a mycoinsecticide were developed. Application techniques were improved by altering equipment and spray strategies through field testing and computer modeling (Galaini-Wraight et al., in press a). Four applications of a commercial standard pesticide (Pydrin/piperonyl butoxide [PBO]) were compared with five applications of B. bassiana during the first Colorado potato beetle generation and two Pydrin/PBO sprays versus three B. bassiana applications in the second Colorado potato beetle generation. Results indicate that B. bassiana is capable of providing reasonable protection of potato foliage in the study plots (Table 20-2) (Galaini-Wraight et al., in press a). Mortality of immature Colorado potato beetles in B. bassiana-treated plots was only slightly lower than that in the insecticide-treated plots and provided total yields about 75 to 80 percent of those achieved in the chemical insecticide treatment (Table 20-3). Adjacent untreated plots were totally destroyed by the Colorado potato beetle and produced no measurable yield. Although B. bassiana was not capable of controlling Colorado potato beetles to the same degree as chemical insecticides were, it clearly provided substantial protection against Colorado potato beetle damage under some conditions. Further refinements in the use of this pathogen as a component of a Colorado potato beetle management program are clearly warranted. A subsequent study, using B. bassiana as a mycoinsecticide on a commercial scale, gave extremely variable results (Hajek et al., 1987).

Variable results have plagued the development and use of mycoinsecticides on a number of crops (McCoy, 1990). Several biological and technical limitations currently exist in using fungi as replacements for insecticides (McCoy, 1990). Although fungal propagules can be applied to crops as an inundative spray, strategies for their use and expectations in terms of the resulting pest mortality and crop protection should be drastically altered

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 20-2 Estimated Percent Mortalities* of Leptinotarsa decemlineata Larvae for Beauveria bassiana and Pydrin/ PBO Treatments

 

Estimated Percent Mortalities

 

First Generation

Second Generation

 

Early Immatures

Late Immatures

Early Immatures

Late Immatures

Plot No.

B. bassiana

Pydrin/PBO

B. bassiana

Pydrin/PBO

B. bassiana

Pydrin/PBO

B. bassiana

Pydrin/PBO

1

77.3

85.6

82.2

84.7

86.1

82.6

21.2

23.0

2

74.7

88.4

82.8

86.6

79.3

79.0

54.8

43.9

3

76.6

87.8

81.1

85.0

82.2

81.4

30.4

51.7

4

81.7

88.2

81.6

90.0

80.9

81.4

30.3

25.3

Mean

77.6a

87.5b

81.9a

86.7b

82.2a

81.1a

33.7b

35.5b

95 percent confidence interval

(72.7–82.2)

(85.4–89.5)

(80.7–83.1)

(82.4–90.4)

(77.3–86.7)

(78.7–83.4)

(13.7–57.4)

(15.4–58.8)

* Percent mortality estimated graphically, as described by T. R. E. Southwood. 1978. Ecological Methods. New York: Chapman and Hall.

Analysis of variance was performed on the mean percent mortalities (arcsine transformed) at alpha = 0.05. Means followed by the same letters within each life stage group of each generation are not significantly different.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

TABLE 20-3 Solanum tuberosum var. Wauseon 1982 Yield Data for Beauveria bassiana and Pydrin/PBO-Treated Field Plots*

 

Yield (lbs/acre [104]) after the Following Treatments

 

B. bassiana

Pydrin/PBO

Plot No.

Salable

Total

Salable

Total

1

1.67

1.84

1.25

1.43

2

1.24

1.42

2.67

2.88

3

1.83

2.02

2.80

3.03

4

2.03

2.25

2.12

2.27

Mean

1.69

1.88

2.21

2.41

Standard error

0.168

0.175

0.352

0.362

* Planted on May 3 and harvested on August 23.

Mean values for B. bassiana versus Pydrin/PBO were not significantly different (p > 0.05, by analysis of variance).

SOURCE: S. Galaini-Wraight, R. I. Carruthers, D. W. Roberts, andM. Semel. In press a. Comparative efficacy of foliar applicationsof Beauveria bassiana conidia and a synthetic pyrethroid against Leptinotarsa decemlineata. Journal of Economic Entomology.

from those for chemical insecticides. Fungal materials may be capable of controlling pests under certain circumstances but not in others. Most importantly, their use should be developed and managed with other control methods in mind, so that truly integrated methods of control can be established rather than just substituting microbials for chemical insecticides.

Enhancement of Naturally Occurring Fungal Pathogens

Depending on the specific details of the host and pathogen population and the associated ecosystem, enhancement of disease development and spread has been accomplished by a number of different methods (Hostetter and Ignoffo, 1978; McCoy et al., 1988). Some specific methods include habitat manipulation, altering cultural practices such as planting or harvesting (Brown and Nordin, 1986), and managing controlled inputs such as irrigation or pesticides (Harem and Hare, 1982; Kish and Allen, 1978; McCoy et al., 1976; Sprenkel et al., 1979). The following discussion of Zoophthora mycosis of the alfalfa weevil is an example of how early harvesting has been used to enhance the effects of naturally occurring populations of this pathogen in an IPM program.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Zoophthora Mycosis of the Alfalfa Weevil

The fungal pathogen Zoophthora phytonomi is known for its natural regulatory effects on populations of the cloverleaf weevil Hypera punctata in North America (Author, 1886a,b; U.S. Department of Agriculture, 1956) and a related weevil species, Hypera variabilis, in Israel (Ben-Zev and Kenneth, 1980). Following the introduction of the alfalfa weevil (Hypera postica) into North America, 17 years of extensive surveys revealed no infections in H. postica populations (Puttler et al., 1978) until 1973, when a pathogen similar to Z. phytonomi was first observed, causing significant epizootics in alfalfa weevil populations throughout southern Ontario, Canada (Harcourt et al., 1974). Harcourt et al. (1984) suggest that this pathogen was one of the primary reasons for the major alfalfa weevil decline seen in Ontario during the mid-1970s. Subsequently, this pathogen spread into other North American alfalfa production areas, where it also caused significant mortality of H. postica (Gardner, 1982; Nordin et al., 1983; Pienkowski and Mehring, 1983; Puttler et al., 1978). Although taxonomic questions still exist, current evidence suggests that the pathogen that infects alfalfa weevils is a different species of Zoophthora than is found to infect the cloverleaf weevil (Harcourt et al., 1981).

It is unclear whether the pathogen that causes mycosis in the alfalfa weevil was introduced into North America in conjunction with weevil introductions or exotic parasite releases or whether the pathogen switched from another North American host species onto H. postica. Although the origin of this pathogen is still unknown (Puttler et al., 1978), the fungus has become well established as a major natural biological control agent of the alfalfa weevil throughout much of its range. Epizootiological studies have shown that disease prevalence varies between sites and seasons, but levels from 30 to 70 percent are not uncommon at the time of peak larval occurrence (Puttler et al., 1980) and have approached 100 percent late in the host's developmental cycle, particularly when densities are high (Harcourt et al., 1974; Nordin et al., 1983). Disease levels of this magnitude produce larval mortalities of between 65 and 90 percent, with an additional 40 to 50 percent expressed in the less visible pupal stage (Harcourt et al., 1974). Brown and Nordin (1982) determined that a threshold host density (1.7 weevils/alfalfa stem) was required for Zoophthora spp. to induce epizootics. Although this threshold varied with environmental moisture, low host densities were thought to limit early-season spread of mycosis. Using laboratory, field, and simulation modeling experiments, Brown and Nordin (1986) developed early harvesting strategies that maximized the development and spread of Zoophthora spp. even when weevil populations were lower than critical levels for epizootic development. This was accomplished by harvesting the alfalfa when Zoophthora mycosis of weevil larvae was

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
×

first observed. Early harvesting is thought to increase disease prevalence because it (1) concentrates larvae in windrows, (2) damages or stresses larvae, making them more susceptible, and (3) alters microenvironmental conditions (increases moisture) to enhance sporulation, germination, and thus, infection. Research fields managed by this technique showed higher disease prevalence, which demonstrates that enhancement of fungal diseases is not only possible but is practical and economical, as it is based on accepted production practices and equipment (Brown and Nordin, 1986). However, a better understanding of the spatial distribution and dynamics of this pathogen is necessary to implement this strategy effectively in a statewide IPM program (Brown and Nordin, 1986).

Introduction of Exotic Fungal Pathogens

Classical biological control (introduction of exotic fungi, either new species or more pathogenic strains of a species that already exists) has received very little attention in the field of insect pathology (Roberts, 1978). Some reports of attempts to establish exotic fungi include the use of Coelomomyces stegomyiae for control of mosquitoes (Laird, 1967), Entomophaga aulicae for control of the browntail moth (Speare and Cooley, 1912), Enromophthora erupta for control of the green apple bug (Dustan, 1923), and Zoophthora radicans for control of the spotted alfalfa aphid (Hall and Dunn, 1957; Milner et al., 1982). Although releases were made in each of these cases, detailed population assessments documenting the effects of these fungi were rarely conducted. The introduction of Zoophthora radicans into the United States provides an example of current research on a introduction of a fungus and its possible impact on the target host population.

Introduction of Zoophthora radicans into the United States

Alfalfa, Medicago sativa, is the world's most valuable forage crop, providing the best food value for all classes of livestock. Forages provide in excess of half the feed units for livestock, which in turn provides half of the nutrients consumed by Americans. In addition to its nutritional value, alfalfa is important because it has high nitrogen-fixing capabilities and because it is a soil-conserving perennial crop. Alfalfa is grown on over 27 million acres in the United States and is exceeded in production acreage only by corn, soybeans, and wheat. Alfalfa, however, exceeds each of these crops in protein output per unit area, producing an overall cash value estimated in excess of $6 billion per year (New York Crop Reporting Service, 1985).

Several insect pest species attack alfalfa throughout the United States,

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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but currently, the potato leafhopper, Empoasca fabae, is considered to be the most serious economic threat (Gyrisco et al., 1978). Feeding by the potato leafhopper causes severe yellowing and stunting both in seedling and established alfalfa stands. Losses combined with control expenditures cost U.S. alfalfa producers millions of dollars annually. Entomologists in Illinois and Wisconsin estimate that in an average season, yields are decreased approximately 20 percent in terms of quantity, with additional losses of approximately 20 percent through reduced protein content. In addition, E. fabae is a major pest in numerous crops (potatoes, soybeans and other beans, clovers, and more than 100 other cultivated plants), causing significant losses (Gyrisco et al., 1978).

Successful biological control agents, both insect parasitoids and microbial pathogens, are currently helping to reduce populations of other major alfalfa pests (e.g., the alfalfa weevil, the pea aphid, and the alfalfa blotch leaf miner) to well below economic thresholds in many areas of the country (Brown and Nordin, 1982; Dunbar and Hower, 1976; Hower and Davis, 1984). No such biological control organisms are being used to manage potato leafhoppers. After 5 years of effort, the European Parasite Laboratory of ARS has terminated its program aimed at locating beneficial insects to control the potato leafhopper. Currently, the only control option for leafhopper management is the application of chemical insecticides, which is not only costly but also interferes with other highly successful biological control programs for alfalfa. More insecticides are now being applied to alfalfa in the central and eastern United States to control E. fabae than are being used to control all other insect pests combined. Microbial control of E. fabae may provide an alternate management tool in the alfalfa production system that would be more compatible with existing alfalfa pest management programs, provide less of a hazard to livestock, and in general, would be more sound environmentally.

Initial research on the effects of Zoophthora radicans on Empoasca fabae was conducted through cooperative efforts of various agencies including ARS, the Cooperative State Research Service, and the U.S. Agency for International Development. The Plant Protection Research Unit, ARS, USDA, joined in an effort with the Boyce Thompson Institute for Plant Research, the Illinois Natural History Survey, and Cornell University to explore the possibility of microbial control of the potato leafhopper by using Z. radicans isolates collected from a related leafhopper species in Brazil. Through efforts made in this program, it became clear that Z. radicans had significant potential for the biological control of E. fabae (Galaini-Wraight et al., in press b; McGuire et al., 1987a,b; Wraight et al., 1986).

Epizootic levels of Z. radicans are commonly seen in Brazilian leafhopper populations and are known to cause significant population reductions in both bean and cowpea crops (Galaini-Wraight et al., in press b).

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Pathogen isolates from these epizootics were imported to the United States and tested against the potato leafhopper under laboratory conditions at the Boyce Thompson Institute for Plant Research. These studies show that pathogen levels as low as 3.3 spores/square millimeter cause significant levels of infection (greater than 70 percent) in late-instar nymphs (Figure 20-4). A 10-fold increase in dose (33.0 spores/square millimeter) repeatedly caused 100 percent mortality. Time from infection to host death and secondary spore production (pathogen multiplication) is very rapid, 2 to 4 days, depending on host age and environmental conditions.

Z. radicans is a very attractive pathogen for use as a biological control, as it may either be introduced in an inoculative release or be used more as a microbial pesticide (inundative release). This pathogen can be easily produced in large quantities and stored for relatively long periods of time by using the marcesence technology developed by the Plant Protection Research Unit of ARS (R. S. Soper and D. M. McCabe, USDA patent 4,530,834). Fungal mycelium can be grown in liquid medium, dried, milled, stored, and then applied in the field, where it rehydrates and produces infective conidia in patterns very similar to those of fungi grown directly from a newly killed host.

FIGURE 20-4 Laboratory dose-mortality relationship between Zoophthora radicans and the potato leafhopper Empoasca fabae.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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This material has been applied to small field plots and evaluated for its sporulation potential and pathogenicity to caged populations of E. fabae. These studies not only showed primary infection levels as high as 70 percent in caged leafhoppers within 24 hours but also high infection levels in natural populations through inadvertent mycosis of leafhoppers outside the test cages. Inoculation densities of approximately 5.0 grams of dried hyphae per square meter were applied to a total of 12 square meters, inducing infection levels as high as 92 percent across a 0.75-acre test field over a 3-week sample period (Figure 20-5). The epizootic reduced leafhopper populations from 1.7 to 0.08 leafhoppers per stem—a 95 percent reduction. A second study conducted in an adjacent field gave similar results.

In Illinois, a similar release (using infected cadavers in a potato field) produced the same general results (McGuire et al., 1987b). Although not clearly documented in the year of release, Z. radicans became established in central Illinois and has caused substantial epizootics in leafhopper populations over the last few seasons. Infection levels as high as 90 percent have been recorded among leafhoppers in beans, where the epizootics have been most evident. Since its introduction into Illinois, Z. radicans has spread approximately 20 miles from the original release sites and has caused major leafhopper declines in bean, potato, and alfalfa crops. Additional introductions in Illinois have continued to cause similar epizootics.

In 1979, different isolates of this same pathogen were introduced into New South Wales, Australia, in a cooperative effort between the Plant Protection Research Unit, ARS, USDA, and Commonwealth Scientific and Industrial Research Organization (CSIRO) for biological control of the spotted alfalfa aphid (Milner and Soper, 1981). Z. radicans quickly became established in New South Wales, caused epizootics in the pest population, and spread over 200 miles from the original release site. In the third field season, Z. radicans was again found to induce epizootics (up to 74 percent prevalence) in sampled spotted alfalfa aphid populations (Milner and Lutton, 1986) and has spread over 186 miles from the original release sites (Milner and Lutton, 1983; Milner and Soper, 1981; Milner et al., 1980, 1982; R. J. Milner, CSIRO, personal communication, 1989). Clearly, a similar potential exists for Z. radicans to become a major biological control agent against E. fabae throughout its U.S. distribution.

Although a single isolate of Z. radicans has shown significant potential to control E. fabae under natural field conditions, several additional isolates have been collected from South America and Europe. A number of these isolates have shown equal or higher pathogenicity to E. fabae in laboratory screenings than the material originally tested and released in the field. These isolates may also possess other beneficial characteristics, such as a faster speed of kill or better overwintering ability, which are yet to be evaluated. Screening of this germ plasm in the laboratory is under way, and further evaluation of selected pathogen isolates will be conducted in the field following approval by APHIS, USDA, and the U.S. Environmental Agency. It
Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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FIGURE 20-5 Example epizootic of Erynia radicans in a natural population of Empoasca fabae in a 0.75-acre alfalfa field. A total of 60 grams of dried mycelium was applied to the three blocks (12 square meters) marked in the lower right corner. This small amount of fungal material multiplied rapidly, causing almost a complete decline in the leafhopper population in this field. Leafhoppers in an adjacent 1.0-acre field were also decimated. PLH, potato leafhoppers.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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is hoped that these studies will allow the introduction and establishment of Z. radicans as a biological control agent throughout the full geographic range of the potato leafhopper (Carruthers and Soper, 1987).

CONCLUSION, RESEARCH NEEDS, AND FUTURE APPLICATIONS OF BIOTECHNOLOGY

Entomopathogenic fungi are important natural regulators of many arthropod populations, including several pest species. A variety of strategies have been used successfully to manipulate fungi in biological control programs. While there have been fewer documented biological control successes with fungal pathogens than with parasitoids and predators, much less effort and capital have been expended to understand and manage them. Most of the research conducted on fungal pathogens of insects has emphasized the use of these organisms as microbial insecticides. Application of pathogens by inundative release may indeed prove to be a useful tactic, but fungi should not be considered as direct replacements for chemical insecticides. Fungi are complex organisms that interact with their hosts and the environment in intricate ways. Intelligent use of fungi as biological control agents will require detailed knowledge of their pathobiology, epizootiology, and interactions with other components of the ecosystems in which they are to be used. This will become increasingly important as scientists begin to alter fungal pathogens genetically to improve their efficacy as biological control agents.

Admittedly, fungi are limited in their ability to control insect pests. For example, not all pest species are susceptible to fungal pathogens, and even if they are susceptible, the target hosts may live in an environment that is not conducive to fungal infection and transmission. As mentioned previously, fungal pathogens are highly dependent on moisture for spore germination and infection to proceed. They are also adversely affected by high temperatures. Pest control with any biological control agent will not be as certain or repeatable as the action of chemical insecticides. For this reason, expectations need to be altered, integrated control programs need to be developed by using multiple tactics, and efficiency in the use of fungi and other pathogens as biological control agents needs to be continued. Most importantly, a research agenda should be developed that is aimed at solving specific problems associated with the development and application of microbial agents for biological control.

Although the list of needed research on fungal pathogens and their use in biological control is long, five specific areas need additional attention.

  1. It is important that fungal pathogen germ plasm be collected now and preserved for future evaluation and use.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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  1. Continued expansion of research on fungal epizootiology and ecology is needed so that disease dynamics, the impact of pathogens on host populations, and the factors that limit disease development and spread under field conditions can be understood.

  2. The genetic aspects of host and pathogen populations that affect the establishment, spread, and maintenance of disease in insect populations need to be studied. It must be recognized that natural populations of fungal pathogens contain high levels of genetic variation that could contribute to their ability to regulate host populations. Furthermore, the potential for the evolution of resistance in the host population must be explored before it becomes a problem in the field.

  3. Efforts to integrate the use of pathogens with other control tactics must be increased. Until control efforts use multiple tactics to manage a complex of pest species, IPM will remain in its infancy.

  4. The use of innovative techniques in addressing problems associated with biological control agents needs to be expanded.

New biotechnologies provide the tools needed to answer questions that have never been able to be asked before. It is expected that innovative biological techniques can be used to manipulate desirable traits, and thus improve the effectiveness of some fungal pathogens. Recombinant DNA techniques are being used to study the mechanisms of pathogenicity and virulence at the molecular level. For example, fungal enzymes and associated genes involved in penetration of the insect cuticle have been identified (St. Leger et al., 1987, 1988b). Knowledge of these genes and gene products may eventually lead to genetic alteration of fungal pathogens. By using transformation systems developed for other types of fungi (Shimizu, 1987; Yoder et al., 1987), it may be possible to clone the genes responsible for these products and transfer them to fungi that may have poor penetration ability but that are well adapted to a particular environment. The genes involved in toxin production are also candidates for cloning.

Biotechnological methods are also being applied to improve methods for field monitoring of insect fungal diseases. Enzyme-linked immunosorbent assays are used to detect a variety of fungi in plant tissues (Mendgen, 1986) and have shown promise for detecting fungal cells of Entomophaga maimaiga in gypsy moth larval hemolymph (Hajek et al., 1988). Other techniques such as isoenzyme polymorphisms (Boucias et al., 1982; Micales et al., 1986) and restriction fragment length polymorphisms will become increasingly useful in detecting different fungal pathogen strains.

It is important, however, that researchers do not get lost in the techniques and lose sight of the important question: How can the ability to manage pest problems be improved while improving both the economic and environmental situation? Despite the promise of new technologies, success-

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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ful biological control depends on a fundamental knowledge of host and pathogen biology, not only at the molecular level but at the cellular, organismal, population, and ecosystem levels as well. It is evident that specialists from many subdisciplines of entomology, genetics, mycology, systems science, and other fields of study will be required to identify, manipulate, and use fungi successfully for biological control purposes in the future.

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Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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21

Reactors' Comments

Time Frame for Sustainable Agriculture and Pollution Prevention Research

Clayton W. Ogg

The research on the Northeast region presented in this volume emphasized the complexities of managing biologically interrelated systems in a dynamic farm setting. Earlier chapters in this volume describing other regions of the United States found similar challenges; but organic approaches, eutrophic livestock operations, and insect management using fungi addressed in the three chapters on research in the Northeast region present special challenges. Clearly, a longer-term research focus is required in these most challenging areas of sustainable agriculture research.

Other sustainable agriculture projects offer more immediate dividends. An earlier chapter in this volume by Paul Johnson described an aggressive, short-term research and education program in Iowa focusing on selected sustainable agriculture activities. Iowa's program provides substantial resources to calibrate one of the more promising sustainable agriculture technologies for statewide use, focusing on soil testing for nitrogen.

Without in any way challenging the need for longer-term research, it may be useful to explore nearer-term roles for sustainable agriculture research and education programs and to compare them with other policies currently under consideration that address pollution from agriculture. This review describes potential sustainable agriculture contributions to pollution prevention that are perhaps capable of avoiding some risks and remediation

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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costs even before these costs are fully quantified. A brief discussion of short-term versus long-term research strategies is also provided.

SUSTAINABLE AGRICULTURE AS A PREVENTION STRATEGY

Sustainable agriculture practices are targeted to farmers who can benefit from reductions in the use of potential pollutants. Sustainable agriculture offers an opportunity for pollution prevention because it prevents pollution from happening in the first place rather than pinpointing the source of an existing environmental problem and targeting action on the basis of where the problem has occurred. The two forms of targeting (targeting of receptive farmers versus targeting of existing environmental problems) work well together, but prevention initiatives can move forward even when costs or the time required to locate pollution sources precisely are prohibitive.

The pollution prevention strategy becomes most attractive when (1) one source may be implicated in multiple environmental concerns, (2) costs are low or actually favor adoption of the practices associated with prevention, (3) the problem is pervasive, and (4) considerable uncertainty exists as to the environmental risks posed by the existing practices. In agriculture, these four conditions appear to exist widely.

With regard to pesticides, reduction of their use may clearly alleviate multiple concerns, fulfilling condition 1 above. These concerns include potential health risks to farmers and workers, potential ecological effects, and potential human health effects from the consumption of residues on food or in the drinking water. A prevention approach may address several problems by reducing the need for a particular chemical.

Condition 2, economic feasibility, is fundamental to the sustainable agriculture concepts presented throughout this volume and needs no elaboration.

Condition 3 for favoring a prevention strategy is the presence of a pervasive problem. In assessing pollution problems in response to Section 319 of the Clean Water Act (P.L. 100-4), the states find that over half of the water bodies that have been assessed so far (which include about 41 percent of the total water bodies in the United States) are impaired by nutrients (U.S. Environmental Protection Agency, 1989); the Resources Conservation Act study conducted by the U.S. Department of Agriculture (1989) estimated that 70 percent of phosphorus now in streams originates from agricultural activities. Phosphorus presents the main nutrient problem in surface water. Yet, in some intensively farmed regions, nitrogen pollution of groundwater is also pervasive, with 5 to 20 percent of wells tested exceeding health advisory levels for nitrates (Madison and Brunett, 1985). For pesticides, a U.S. Geological Survey study (Goolesby et al., 1989) cited in other chapters in this volume and another recent study by Richards and

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Baker (1989) suggest that pesticides occur above health advisory levels in streams, larger rivers, and according to Richards and Baker (1989), drinking water. All of these problems are concentrated in certain regions, where prevention becomes a particularly appropriate strategy: Farms that potentially benefit from prevention research and education in such regions likely contribute to one or several of the more common pollution problems.

Finally, uncertainties regarding the health effects and the ensuing remFediation costs (condition 4 above) favor a prevention strategy. Many of the occurrences of substances in water described above are at levels at which considerable uncertainty exists as to their effects on human health, leading to ongoing study and debate as to what level of the substances should be permitted in drinking water. Lower-bound cost estimates for carrying out requirements under the Safe Drinking Water Act (P.L. 99-339) are nearly $1 billion per year. Costs will escalate to several billion dollars a year if safety standards for nitrates are lowered or if pesticides in surface water systems prove to be a widespread problem (Wade Miller Associates, 1989a,b). A prevention strategy has particular appeal when difficult choices can be avoided through the development and widespread adoption of low-chemical-input farming methods. The low-input sustainable agriculture research and education program is proving to be effective in developing farming systems that increase net farm income while advancing a wide range of environmental goals.

TIME FRAMES FOR SUSTAINABLE RESEARCH AND EDUCATION

The pervasiveness of chemical contamination problems and the uncertainties regarding their health ramifications and potential costs of remediation (Wade Miller Associates, 1989b) lend an urgency to prevention efforts. However, past and ongoing long-term research programs in such areas as soil testing and integrated pest management provide some of the most promising sustainable farming methods available today. The long-term research projects identified in the chapter by Rhonda R. Janke and colleagues and other investigators are needed, but so are the more aggressive shorter-term research and education programs, such as those currently under way in Iowa.

Pennsylvania farmers reduced their use of nitrogen fertilizers state-wide by 52 percent (Berry and Hargett, 1984, 1988) between 1982 and 1988. This was a very welcome development in a state that is located on the Susquehanna River and that is above the ecologically rich and economically valuable waters of the Chesapeake Bay. Much of this reduction may have resulted from a variety of technologies introduced in Pennsylvania to more accurately account for the nitrogen available in the soil from the previous

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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crop year and from applied manure (Fox and Piekielek, 1983). Research by Fox and colleagues has resulted in a soil test that was introduced in 1989 that will lead to an even greater efficiency of nitrogen fertilizer use (Fox and Piekielek, 1978a,b, 1984; Fox et al, 1989; Iversen et al., 1985; Michrina et al., 1981, 1982). Some fertilizer reductions have apparently been accomplished by farmers who learned that the available nitrogen from animal waste on their farms was more than adequate to meet crop needs.

The costs of developing and bringing these and many other sustainable technologies to farmers are very low relative to cost estimates for remediation (Wade Miller Associates, 1989a). Within the context of existing research and education programs, calibration of existing sustainable technologies, such as appropriate soil tests and a number of closely related nitrogen management technologies, merits particular consideration. Also important are expanded education programs that deliver these and other sustainable technologies to farmers.

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Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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U.S. Department of Agriculture. 1989. The Second RCA Appraisal: Soil, Water and Related Resources on Nonfederal Land in the United States—Analysis of Conditions and Trends. Washington, D.C.: U.S. Government Printing Office.

U.S. Environmental Protection Agency. 1989. National Water Quality Inventory—1988 Report to Congress. Washington, D.C.: U.S. Government Printing Office.

Wade Miller Associates. 1989a. Regulatory impact analysis of proposed national primary drinking water regulation for inorganic chemicals. Prepared for Office of Drinking Water, U.S. Environmental Protection Agency, Washington, D.C.

Wade Miller Associates. 1989b. Regulatory impact analysis of proposed national primary drinking water regulation for synthetic organic chemicals. Prepared for Office of Drinking Water, U.S. Environmental Protection Agency, Washington, D.C.

Sustainable Agriculture Research and Education in the Northeast

James F. Parr

By most definitions, sustainable agriculture is viewed as a concept that comprises two major components: i.e. economic sustainability and environmental sustainability (some even emphasize the importance of social and political sustainability). For example, a farming system may be economically sustainable, but if it contributes to environmental degradation, it is not truly a sustainable system. By the same token, a farming system may be environmentally sustainable, but if it is not profitable, then, by definition, it is not a sustainable system.

Sustainability can also be thought of as a long-term goal that seeks to overcome the problems and constraints that afflict both U.S. agriculture and agriculture worldwide. How and whether this goal is achieved depends on the development of alternative management practices that are resource-conserving, energy-saving, economically viable, environmentally sound, and protecting of human and animal health.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Many have developed rather strong opinions on just what a sustainable farming system should be. However, the concept of sustainability involves a time dimension that will most certainly bring about changes that will test the sustainability of farming systems in the years ahead. What is judged to be a sustainable farming system today may not be sustainable in the future because of increased energy costs, global warming, increased soil salinization, and issues of food safety and quality.

As the world population increases and with the continuing decline in the per capita production of food in many developing countries, the natural resource base in the United States and throughout the world will come under greater pressure than ever before. Those farming systems that currently sustain the world's population may very likely be inadequate to do so in the future. There must begin to be a more futuristic attitude about what research and education programs for sustainable agriculture are needed now, so that entirely new and sustainable farming systems can be developed for the future.

LONG-TERM, LOW-INPUT CROPPING SYSTEMS RESEARCH

The long-term cropping systems research study, also referred to as a conversion or transition experiment, was implemented at the Rodale Research Center in 1981 when it became apparent that farmers experienced problems when shifting from chemical-intensive farming to low-input (or low-chemical) systems. According to the 1980 USDA Report and Recommendations on Organic Farming (U.S. Department of Agriculture, 1980) the first 3 years of such a transition were often critical and the most difficult to cope with. Weeds were often cited as the main problem, but other chemical and biological factors were also suggested as possible causes.

Good research begins by asking the right questions, and the transition experiment described by Rhonda R. Janke and colleagues was designed to do exactly that. There was also a need to study farming systems holistically so that the interactions of the components could be evaluated. The following farming systems are being studied:

  1. low-input/sustainable, with animals;

  2. low-input/sustainable, cash grain; and

  3. conventional cash grain.

Long-term experiments such as these are essential because significant changes in the chemical, physical, and biological components may not be detectable over the short term. The systems approach that this study uses allows researchers to know not just what happens, but why it happens.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Herein is the very basis for controlling and manipulating the system to the best advantage. A thorough economic analysis of this study is anxiously awaited.

PERSPECTIVES FOR SUSTAINABLE AGRICULTURE FROM NUTRIENT MANAGEMENT EXPERIENCES IN PENNSYLVANIA

This chapter reported on the management practices of some dairy farms in the Northeast region where there has been a steady increase in nutrient levels on the farm because of a one-way flow of off-farm purchased inputs. According to the author, Les E. Lanyon, many of these farms now import all feed sources for the dairy cows, with little or no on-farm production of feed grains or forages. This has resulted in an excess of manure that is then applied back to the land as a disposal medium. Thus, over a period of time, nutrient-poor farms have become nutrient-rich farms or, indeed, eutrophic farms.

The chapter presents some strategies for dealing with this problem which, if it is not a real pollution problem, it is certainly a potential pollution hazard, especially to groundwater from excess nitrates. The chapter describes crop rotation scenarios that can help to utilize the accumulated nutrients while demonstrating economic benefits.

Agriculture is a system of inputs (some of which are purchased) and outputs (some of which are sold and removed from the farm). Generally, there is a net removal of nutrients during the production cycle. The dairy farms described in this chapter have a net gain of nutrients and a gross imbalance that must be managed properly to avoid a serious pollution problem. When excessive amounts of organic nitrogenous materials such as manure are applied to soil, serious water pollution problems can result, just as they can from improper use of chemical nitrogen fertilizers. These farms may be economically viable, but they definitely are not sustainable farming systems.

The question is, to what extent are these farms already polluting groundwater? Nitrate concentrations should be monitored in both soils and well water, and if they are excessive, remedial action should be taken to alleviate this situation.

USE OF FUNGAL PATHOGENS FOR BIOLOGICAL CONTROL OF INSECT PESTS

Raymond I. Carruthers and colleagues point out that certain fungal pathogens have the potential to control insect pests and can greatly enhance integrated pest management programs and reduce pesticide use. Such fungal pathogens must be environmentally acceptable, cost-effective, reliable, and dependable and must not attack other beneficial natural predators.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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It may be necessary to manipulate fungal pathogens to achieve the most effective control measures. Strategies for biological manipulation and control include germplasm maintenance, disease dynamics, use of population genetics of pathogens and hosts, and integration with other control strategies such as integrated pest management.

The new biotechnologies should be useful tools in future efforts to enhance the reliability and effectiveness of this unique biological control strategy.

REFERENCE

U.S. Department of Agriculture. 1980. USDA Report and Recommendations on Organic Farming. Washington, D.C.: U.S. Government Printing Office. 164 pp.

Sustainable Agriculture Research and Education in the Field

Neil H. Pelsue, Jr.

I am impressed by the information presented in this volume. It is especially impressive to know that this work is representative of a much larger body of work going on throughout the United States.

I applaud the discussion by Michael Duffy presented in this volume. His comments were especially appropriate because system sustainability needs to receive much more attention than it has up to now. That is my bias in my assessment of the potential contributions of projects to sustainable agriculture goals.

In the following sections, I address the three projects in the Northeast described by Rhonda R. Janke and colleagues, Les E. Lanyon, and Raymond I. Carruthers and colleagues. I will not discuss project methodology, as that should have been well covered in the project evaluation and selection process. Rather, I will focus on four other aspects that I believe are important criteria for low-input sustainable agriculture (LISA):

  1. whole-farm interactions,

  2. economic performance,

  3. environmental impact, and

  4. information delivery.

To my way of thinking, the fourth essential aspect—delivery of project

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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information to farmers and other users in readily usable form—was not adequately discussed in any of the three presentations.

LONG-TERM, LOW-INPUT CROPPING SYSTEMS RESEARCH

Whole-Farm Interactions: This project includes several cash grain systems and incorporates a livestock component to provide comparisons with conventional grain-livestock systems. The project makes good use of farmer inputs in project development and system assessment.

Economic Performance: This project makes a good attempt at estimating the conversion costs for farmers as they move from conventional to alternative systems. I would encourage that component analyses (corn) be integrated into a systems analysis to estimate interaction effects. This is a good use of FINPACK (Hawkins et al., 1987) (or other computer software) for analyzing the financial implications of alternative farm management decisions.

Environmental Impact: Important objectives of the project are to reduce chemical use, observe nitrogen recycling, and determine the water-handling capacities of soils.

PERSPECTIVES FOR SUSTAINABLE AGRICULTURE FROM NUTRIENT MANAGEMENT EXPERIENCES IN PENNSYLVANIA

Whole-Farm Interactions: This project studies farm management activity flows and the interactions of production components.

Economic Performance: While the project compares on-farm manure use in financial terms, it lacks the necessary comprehensive economic assessment.

Environmental Impact: The project recognizes the need to identify the environmental effects of on-farm manure use both on and off the farm.

This chapter provided a good overview of the process that was used to select components to improve the system, but it did not provide specifics about the nutrient management project.

USE OF FUNGAL PATHOGENS FOR BIOLOGICAL CONTROL OF INSECT PESTS

Whole-Farm Interactions: This chapter provided some of the necessary, basic information that will need to be integrated into whole-farm systems.

Economic Performance: The project needs to demonstrate the economic effectiveness of biological control technology before large commitments are made to further research.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Environmental Impact: The chapter stressed the importance of evaluating how alternative pest control methods are used and their interactive effects.

ADDITIONAL ECONOMIC FEASIBILITY STUDIES

Additional work is needed to assess adequately the ecomomic feasibility of sustainable agriculture studies and projects currently being carried out. This economic analysis can be divided into five categories.

On-Farm Analysis

There will continue to be a need for traditional partial and enterprise budgeting analyses to determine the economic impact of a particular practice (Osburn and Schneeberger, 1978). Essential component analysis is also needed to assess the overall impact of input changes to the farm business operation.

Infrastructural Analysis

Infrastructural analysis refers to assessing the nature and extent of the economic impact on those sectors that provide farm production inputs: the manufacturers and suppliers. At the other end of the production process, the economic effects on marketing activities, processing, and commodity handling also need to be assessed. This analysis also includes government policies, because of the powerful impact of government actions on economic viability.

Consumer Analysis

Other factors that must be taken into account are the reactions of consumers to changes in product prices and to the quantity, quality, and variety of the available food and fiber products. The nature and extent of consumer demand is as important a determinant of economic viability as is production efficiency. However, consumer demand often gets overlooked or taken for granted in analyses of alternative agriculture practices.

Societal Analysis

Another important, but conceptually difficult, aspect is the determination of socioeconomic costs as communities and rural areas are affected by changes in the structure of the agricultural industry.

Suggested Citation:"PART FIVE: RESEARCH AND EDUCATION IN THE NORTHEASTERN REGION." National Research Council. 1991. Sustainable Agriculture Research and Education in the Field: A Proceedings. Washington, DC: The National Academies Press. doi: 10.17226/1854.
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Environmental Analysis

It is necessary to determine the economic impact of agricultural practices as they apply to environmental considerations of both on-farm and off-farm aspects of the production and marketing of food and fiber products. What are now referred to as externalities need to be incorporated into the economic modeling systems (Barlowe, 1986).

INFORMATION DELIVERY

One of the most important objectives of LISA and related programs is to get study results to users in a timely and usable fashion. Farmers, researchers, and members of industry must be able to take advantage of proven and available information delivery systems, developing new or modified systems only as the existing systems are shown to be inadequate.

REFERENCES

Barlowe, R. 1986. Land Resource Economics, 4th ed. Englewood Cliffs, N.J.: Prentice-Hall.

Hawkins, R. O., D. W. Nordquist, R. H. Craven, J. A. Yates, and K. S. Klair. 1987. An Overview of FINPACK. St. Paul, Minn.: Center for Farm Financial Management, Minnesota Extension Service, University of Minnesota.

Osburn, D. D., and K. C. Schneeberger. 1978. Modern Agriculture Management. Reston, Va.: Reston Publishing Co., Prentice-Hall.

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Next: PART SIX: SUMMARY »
Sustainable Agriculture Research and Education in the Field: A Proceedings Get This Book
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Interest is growing in sustainable agriculture, which involves the use of productive and profitable farming practices that take advantage of natural biological processes to conserve resources, reduce inputs, protect the environment, and enhance public health. Continuing research is helping to demonstrate the ways that many factors—economics, biology, policy, and tradition—interact in sustainable agriculture systems.

This book contains the proceedings of a workshop on the findings of a broad range of research projects funded by the U.S. Department of Agriculture. The areas of study, such as integrated pest management, alternative cropping and tillage systems, and comparisons with more conventional approaches, are essential to developing and adopting profitable and sustainable farming systems.

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