|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 239
Prepublication Copy—Subject to Further Editorial Correction
G
Life-Cycle Inputs for Production of Biomass
Nitrogen and phosphorus are the nutrients required in the largest amounts to
sustain biomass-crop growth and development, and they have the greatest environmental
impact. Nitrogen is leached below the crop root zone into subsurface tile drainage lines or
groundwater, and phosphorus moves in runoff. Both nutrients cause eutrophication of
water bodies, which contributes to such problems as hypoxia in the Mississippi River
watershed and the hypoxic region (“dead zone”) of the Gulf of Mexico.
Nitrogen, phosphorus, and other crop-production inputs should be applied at
economically optimal rates rather than at rates that will achieve the highest yields.
Phosphorus and potassium rates are generally based on soil test levels that have been
optimized for each state. For Iowa, application of phosphorus pentoxide (P2O5) fertilizer
for corn grown in soils with optimal, low, or very low soil test ratings (26-35, 16-25, and
0-15 ppm, respectively) would be at 55, 75, or 100 lb/acre. Similarly, application of
potassium oxide (K2O) rate in soils with optimal, low, or very low soil test ratings (131-
170, 91-130, or less than 90 ppm, respectively) would be at 45, 90, or 130 lb/ acre. For
soils testing high or very high in phosphorus or potassium, fertilizer would not be
recommended (Mallarino, 2002)(Mallarino, 2002), assuming that corn residues are not
removed.
The specific nitrogen fertilizer rate required to achieve the maximal economic net
return to nitrogen (MRTN) will vary according to seasonal weather pattern, soil type,
fertilizer price, management practices, and interactions among these factors. For Iowa,
the MRTN for continuous corn or a corn-soybean rotation has been 175 or 125 lb/acre,
respectively, for the last 10 years (Sawyer and Randall, 2008), assuming no harvest of
crop residue.
Recent field studies (Karlen, 2007) indicated that nitrogen, phosphorus, and
potassium removal with the cob and upper portion of the corn plant averaged 10, 2, and
13 lb/ton of dry stover, respectively. The baseline assessment is based on the assumptions
that soils from which crop residues would be removed would have optimal phosphorus
and potassium soil test levels and that nitrogen was being applied at the MRTN.
Therefore, for a stover harvest rate of 1.5 tons/acre, the annual fertilizer requirements of
nitrogen, phosphorus, and potassium would be 190, 27, and 57 lb/acre, respectively, for
239
OCR for page 240
Prepublication Copy—Subject to Further Editorial Correction
continuous corn or 140, 27, and 57 lb/acre for corn rotated with soybean. For 2020
projections (2.5 tons of dry stover per acre), the panel increased fertilizer input to account
for nutrient removal and assumed only a slight increase (10 percent) in MRTN because of
better efficiency of nitrogen use. That resulted in estimated fertilizer requirements of
nitrogen, phosphorus, and potassium of 218, 29, and 69 lb/acre for continuous corn.
Inputs would be much lower for dedicated perennial biomass crops. Woody crops
are rarely fertilized. Herbaceous perennial crops would be harvested when senescent, so
loss of nitrogen, phosphorus, and other nutrients would be minimized because plants
retranslocate such nutrients to roots in fall. The panel envisions a process in which
biofuel processing facilities capture those nutrients, which can then be periodically
returned to the soil. Given the ability of perennial grasses to maintain yields for many
years with little or no fertilization, it might be feasible to return removed nutrients once
every 3-5 years and thus reduce energy requirements for fertilizer transport and
application. Commercial nitrogen fertilizer is energetically expensive but could be
replaced, if needed, by growing one or more legume species with a biomass crop.
Competition between the crop and the legume could be minimized, if competition occurs,
by using a legume that has a different season of maximal growth from the biomass crop.
240
OCR for page 241
Prepublication Copy—Subject to Further Editorial Correction
REFERENCES
Karlen, D. L. 2007. Balancing bioenergy opportunities on your natural resources base.
Paper read at Indiana Crop Advisors Conference Meeting Proceedings on
December 18-19, 2007, at Indianapolis.
Mallarino, A.P., D.J. Wittry, and P.A. Barbagelata. 2002. Iowa soil-test field calibration
research update: Potassium and the Mehlich-3 ICP phosphorus test. North Central
Extension-Industry Soil Fertility Conference 18:30-39.
Sawyer, J.E. and G.W. Randall. 2008. Final Report: Gulf Hypoxia and Local Water
Quality Concerns Workshop. St. Joseph: Upper Mississippi River Sub-basin
Hypoxia Nutrient Committee, American Society of Argricultural and Biological
Engineering.
241
