Corn stover harvest and N losses in central Iowa

Authors: Malone, Robert - Rob; HERBSTRITT, STEPH - Pennsylvania State University; Ma, Liwang; RICHARD, TOM - Pennsylvania State University; CIBIN, RAJ - Pennsylvania State University; GASSMAN, PHIL - Iowa State University; Zhang, Huihui; Karlen, Douglas; Hatfield, Jerry; OBRYCKI, JOHN - Orise Fellow; HELMERS, MATT - Iowa State University; Jaynes, Dan; Kaspar, Thomas; Parkin, Timothy

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2019
Publication Date: 5/1/2019
Citation: Malone, R.W., Herbstritt, S., Ma, L., Richard, T., Cibin, R., Gassman, P., Zhang, H., Karlen, D.L., Hatfield, J.L., Obrycki, J., Helmers, M., Jaynes, D.B., Kaspar, T.C., Parkin, T.B. 2019. Corn stover harvest and N losses in central Iowa. Science of the Total Environment. 663:776-792. https://doi.org/10.1016/j.scitotenv.2019.01.328.
DOI: https://doi.org/10.1016/j.scitotenv.2019.01.328

Interpretive Summary: Corn stover consists of the leaves, stalks, and cobs of corn plants that are generally left in a field after harvest. Harvesting corn stover for bioenergy feedstock is projected to increase over the next few decades. Because of projections of increasing fertilizer nitrogen (N) use and the associated environmental problems, the U.S. National Academy of Engineering has listed “Manage the Nitrogen Cycle” as one of 14 grand challenges for the 21st century. While it is known that corn stover harvest removes nutrients such as nitrogen from fields, the effects on subsurface drainage and other N losses is uncertain. To maintain acceptable corn production, most published modeling studies have assumed supplemental N fertilizer is required to replace the N removed. We used the Root Zone Water Quality Model (RZWQM) to examine N losses with 0 or 50% corn stover removal within a corn and soybean rotation over a 10-yr period from 2001-2010. In general, all simulations used the same 5-day pre-corn-planting or 30-day post-corn-emergence N fertilizer rate of 200 kg ha-1 yr-1. The simulated annual corn yields were nearly the same with or without stover harvest. Accounting for N in the corn stover for the pre-plant scenarios, average total N input during corn years was 19.3 kg N ha-1 greater for 0% than 50% corn stover harvest, but drainage N loss only increased by 1.1 kg N ha-1 yr-1. In comparison, post-emergence N application with no residue removal reduced average drainage N loss by 16.5 kg ha-1 yr-1 compared to pre-plant N fertilization with no residue removal. Not considering any downstream logistics or energy inputs and processing beyond the farm gate, the net energy ratio to the farm-gate was greatest for the post-emergence N applications with 50% corn stover harvest and lowest for the pre-plant N with no corn stover harvest (14.1 and 10.4 MJ output per MJ input). Energy inputs considered in this analysis included on-farm fuel use for planting, crop management and harvest, as well as the embedded energy in inputs such as fertilizers. Energy output was defined as the higher heating value of harvested corn, soybean, and stover biomass. Similar to published studies, the simulations showed little difference in nitrous oxide N emissions to the atmosphere between scenarios, decreased microbial immobilization of N for 50% corn stover harvest compared to no stover harvest, and small soil carbon changes over the 10-yr simulation. In contrast to several previous modeling studies, the crop yield and N lost to drain flow were nearly the same between no corn stover harvest and 50% corn stover harvest if supplemental N was not applied to replace N removed with corn stover. These results are important to optimizing the energy and nitrogen budgets associated with corn stover harvest. This research will help model developers, model users, agricultural scientists and the bioenergy industry more clearly understand N losses and energy budgets under subsurface drained conditions and corn stover harvest, which will help in development of a sustainable bioenergy industry.

Technical Abstract: Corn stover harvest increases N removal from fields, but its effect on subsurface drainage and other N losses is uncertain. We used the Root Zone Water Quality Model (RZWQM) to examine N losses with 0 (NRR) or 50% (RR) corn residue removal within a corn and soybean rotation over a 10-yr period. In general, all simulations used the same pre-plant or post-emergence N fertilizer rate (200 kg ha-1 yr-1 for NRRpre, RRpre, NRRpost, and RRpost). With post-emergence N the simulated annual corn yields averaged 10.7 Mg ha-1 with or without stover harvest, and with pre-plant N the averages were 9.5 and 9.4 Mg ha-1 yr-1 for NRRpre and RRpre. Accounting for corn stover N in the pre-plant scenarios, average total input during corn years was 19.3 kg N ha-1 greater for NRRpre than RRpre but drainage N loss only increased by 1.1 kg ha-1 yr-1. Post-emergence N application with no residue removal (NRRpost) reduced average drainage N loss by 16.5 kg ha-1 yr-1 compared to pre-plant N fertilization (NRRpre). The farm-gate net energy ratio was greatest for RRpost and lowest for NRRpre (14.1 and 10.4 MJ output per MJ input). Similar to published studies, the simulations showed little difference in N2O emissions between scenarios, decreased microbial immobilization for RR compared to NRR, and small soil carbon changes over the 10-yr simulation. In contrast to several previous modeling studies, the crop yield and N lost to drain flow were nearly the same between NRR and RR if supplemental N was not applied to replace N removed with corn stover. These results are important to optimizing the energy and nitrogen budgets associated with corn stover harvest and for developing a sustainable bioenergy industry.