N loss to drain flow and N2O emissions from a corn-soybean rotation with winter rye

Authors: Gillette, Katrina; Malone, Robert - Rob; Kaspar, Thomas; Ma, Liwang; Parkin, Timothy; Jaynes, Dan; FANG, Q - Qingdao Agricultural University; Hatfield, Jerry; Feyereisen, Gary; KERSEBAUM, KURT - Leibniz Centre

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/6/2017
Publication Date: 3/15/2018
Publication URL: https://handle.nal.usda.gov/10113/6557425
Citation: Gillette, K.L., Malone, R.W., Kaspar, T.C., Ma, L., Parkin, T.B., Jaynes, D.B., Fang, Q.X., Hatfield, J.L., Feyereisen, G.W., Kersebaum, K.C. 2018. N loss to drain flow and N2O emissions from a corn-soybean rotation with winter rye. Science of the Total Environment. 618:982-997. https://doi.org/10.1016/j.scitotenv.2017.09.054.
DOI: https://doi.org/10.1016/j.scitotenv.2017.09.054

Interpretive Summary: The role of human activity on the global nitrogen (N) cycle and its effects on the environment such as hypoxia in coastal regions and increased nitrous oxide emissions is of increasing, cross-disciplinary, worldwide concern, and agricultural production is the major contributor. Nitrous oxide (N2O) is a potent greenhouse gas (GHG) and through fertilizer application agriculture is a leading source of N2O emissions. Nitrate loss to subsurface drains in corn and soybean production in the U.S. Midwest is a leading contributor to hypoxia in the northern Gulf of Mexico. With forecasts of increasing fertilizer N use and the associated environmental problems, the National Academy of Engineering listed nitrogen cycle management as one of 14 grand engineering challenges. Including cover crops in corn-soybean rotations reduces N loss to drain flow from agricultural land, but studies are needed to help understand the effects of cover crops under different conditions. Further, only limited studies are available that simultaneously investigate nitrous oxide emissions and nitrate losses to subsurface drain flow. Well tested models help quantify and improve our understanding of nitrous oxide emissions and N loss to drain flow under conditions where field data is limited. We used the Root Zone Water Quality Model (RZWQM) to evaluate nitrate losses to drain flow and nitrous oxide emissions in a corn-soybean system with a winter rye cover crop (CC) in central Iowa over a nine year period. For the most part the model accurately simulated N loss to drainage and N2O emissions over the period of study 2002-2010 and the simulations agree with field data that winter rye cover crop substantially reduces N loss to drainage. In contrast to previous research, monthly nitrous oxide flux was generally greatest when N loss to leaching was greatest, mostly because relatively high rainfall occurred during the months fertilizer was applied. The results suggest that RZWQM is a promising tool to estimate nitrous oxide emissions from subsurface drained corn-soybean rotations in central Iowa and to estimate the relative effects of a winter cover crop over a nine year period on nitrate loss to drain flow. This research will help model developers, model users, and agricultural scientists more clearly understand N2O emissions and nitrate transport under subsurface drained conditions that include a winter rye cover crop, which will help in the design of more effective management to reduce N export to air and water.

Technical Abstract: Anthropogenic perturbation of the global nitrogen cycle and its effects on the environment such as hypoxia in coastal regions and increased N2O emissions is of increasing, cross-disciplinary, worldwide concern, and agricultural production is a major contributor. Only limited studies, however, have simultaneously investigated NO3- losses to subsurface drain flow and N2O emissions under corn-soybean production. We used the Root Zone Water Quality Model (RZWQM) to evaluate NO3- losses to drain flow and N2O emissions in a corn soybean system with a winter rye cover crop (CC) in central Iowa over a nine year period. The observed and simulated average drain flow N concentration reductions from CC were 60 and 54% compared to the no cover crop system (NCC). The model correctly simulated a decrease in annual N concentration differences between NCC and CC over the study period (2002-2010) of approximately 1 mg N L-1 yr-1. Average annual April through October cumulative observed and simulated N2O emissions (2004-2010) were 6.7 and 6.0 kg N2O-N ha-1 yr-1 for NCC, and 6.2 and 7.2 kg N ha-1 for CC. In contrast to previous research, monthly N2O emissions were generally greatest when N loss to leaching were greatest, mostly because relatively high rainfall occurred during the months fertilizer was applied. A local sensitivity analysis suggests that lower soil field capacity affects RZWQM simulations, which includes increased drain flow nitrate concentrations, increased N mineralization, and reduced soil water content. The results suggest that 1) RZWQM is a promising tool to estimate N2O emissions from subsurface drained corn-soybean rotations and to estimate the relative effects of a winter rye cover crop over a nine year period on nitrate loss to drain flow and 2) soil field capacity is an important parameter to model N mineralization and N loss to drain flow.