Optimizing Nutrient Management for Sustainable Bio-energy Feedstock Production

Authors: Kovar, John; Karlen, Douglas

Submitted to: Fluid Journal
Publication Type: Trade Journal
Publication Acceptance Date: 3/31/2010
Publication Date: 4/9/2010
Citation: Kovar, J.L., Karlen, D.L. 2010. Optimizing Nutrient Management for Sustainable Bio-energy Feedstock Production. Fluid Journal. 18(3). Available: http://fluidjournal.org/1gsdgfs-S10/S10-A2.pdf

Interpretive Summary: Growing crops for bio-fuel feedstock production has attracted the attention of many producers – especially in the Corn Belt states. Both corn grain and stover are being evaluated as potential bio-fuel feedstocks. Unfortunately, our understanding of the short- and long-term effects of removing both corn grain and stover on soil nutrient cycling, physical properties, and biological activity is limited. After two years of Iowa field trials, using a variety of management systems including both standard fertilizer management and a high-population treatment with increased nutrient additions, we found that nitrogen (N) and sulfur (S) fertilizer applications were less than needed to carry the corn crop through the growing season. Therefore, crop management did not affect corn grain yields, but plots from which corn stover was not removed during the previous growing season always yielded less than plots from which ~50% or ~90% of the stover was removed. A combination of less fertilizer N and greater tie up in the soil where residues remained probably decreased grain yields. In a separate study, we evaluated the performance of several S fertilizers as S sources for corn grown for bio-fuels. After four years, we found that an application of 30 lb S/A increased grain yield by up to 12 bu./A. Significant soil variability at the research sites may have limited additional crop response to S. For several reasons including erosion of high-fertility hill slope soils, fewer S impurities in fertilizers, and decreased atmospheric deposition of S throughout the upper Midwest, our results suggest that S may quickly become a limiting nutrient for corn grown as a bio-energy feedstock. The results of this research will benefit commercial growers, as well as the fertilizer and ethanol industries, by providing nutrient management guidelines that maximize crop utilization and biomass yields.

Technical Abstract: Corn grain and stover are both being evaluated as feedstock sources for bio-energy production. To meet current and future demands for corn, both short- and long-term effects on nutrient cycling, physical properties, and biological activity in soils must be understood. Our project goal was to increase corn grain and stover yield by optimizing positional and temporal nutrient availability with surface or subsurface bands of N-P-K-S fluid fertilizers. In 2008, first year results for conventional and twin-row management averaged 171 and 183 bu/A, respectively. Dry corn stover yields averaged 2.5, 2.9, 2.8, and 3.1 tons/A for the high (just below ear shank) and low (~4-inch stubble) cuts for the two planting configurations, respectively. Neither management system (including planting configuration, plant population, and fertilization rate) nor tillage (chisel vs no-till) affected corn grain yield in 2009; however, grain yield was lower, averaging 142 bu/A, in plots where corn stover was not harvested in 2008. We attribute this response to the total amount of fertilizer, particularly N, that was applied to the non-removal plots. The amount (160+75+60+20 N+P+K+S, respectively) was based on previous studies. Even though early-season N supply was adequate based on V6 tissue tests, the lower N rate (coupled with increased immobilization during residue decomposition and less mid-season mineralization) negatively affected final corn grain yield. These results suggest that good nutrient management for systems producing both grain and residue feedstock is essential, and that it will differ from grain-only systems. In a separate but related study, corn grain yield on an eroded, low organic matter Clarion soil was increased for the fourth consecutive year in 2009 by applying S at 30 lbs/A. Applying S increased grain yield by as much as 12 bu/A, but so far, no one source has proven superior.