Drainage N loads under climate change with winter rye cover crop in a northern Mississippi River Basin corn-soybean rotation

Authors: Malone, Robert - Rob; Garbrecht, Jurgen; Busteed, Phillip; Hatfield, Jerry; Todey, Dennis; GERLITZ, JADE - Iowa State University; FANG, QX - Chinese Academy Of Sciences; SIMA, MATTHEW - Princeton University; Radke, Anna; Ma, Liwang; QI, ZHIMING - McGill University - Canada; WU, HUAIQING - Iowa State University; Jaynes, Dan; Kaspar, Thomas

Submitted to: Sustainability
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/11/2020
Publication Date: 9/16/2020
Citation: Malone, R.W., Garbrecht, J.D., Busteed, P.R., Hatfield, J.L., Todey, D.P., Gerlitz, J., Fang, Q., Sima, M., Radke, A.G., Ma, L., Qi, Z., Wu, H., Jaynes, D.B., Kaspar, T.C. 2020. Drainage N loads under climate change with winter rye cover crop in a northern Mississippi River Basin corn-soybean rotation. Sustainability. 12(18). Article 7630. https://doi.org/10.3390/su12187630.
DOI: https://doi.org/10.3390/su12187630

Interpretive Summary: Hypoxia or dead zones in coastal oceans have been expanding since the 1960s and are forecast to increase with climate change if reduction strategies are not implemented. Spring nitrate-N loads from the Mississippi River strongly contribute to the size of the hypoxic area in the Gulf of Mexico and reduced nitrate-N loads are needed. To help reduce N loads entering the Gulf of Mexico from the Mississippi River 45% by 2035, Iowa set the goal of reducing non-point source N loads 41% which includes corn and soybean fields with subsurface drainage. Implementing winter rye cover crop into agricultural systems is one of the more promising strategies to reduce N loads to subsurface drainage without reducing cash crop production, but its effectiveness in the Mississippi River Basin under expected climate change is uncertain. We used the tested Root Zone Water Quality Model (RZWQM) to estimate N loads to drainage and crop yield in a central Iowa corn-soybean rotation both with and without winter rye cover crop under 1) baseline weather and CO2 (1991–2011), and 2) projected future temperature and precipitation change and elevated CO2 (2065-2085). N loads to drainage were reduced with cover crop under climate change compared to baseline climate without cover crop more than 41% for at least 18 of the 21 years. Under projected climate change, average annual simulated crop yield between scenarios with and without winter rye were essentially the same. These results suggest that implementing winter rye cover crop in a corn-soybean rotation effectively addresses the goal of N load reduction to drainage under climate change in a northern Mississippi River Basin agricultural system without affecting cash crop production. This research will help decision makers and agricultural scientists more clearly understand nitrate transport reductions to subsurface drainage from including winter rye cover crop in corn-soybean rotations under future climate conditions, which will help in the design of effective management systems to reduce hypoxia in the Gulf of Mexico and reduce N export to the Mississippi River Basin.

Technical Abstract: To help reduce N loads entering the Gulf of Mexico from the Mississippi River 45% by 2035, Iowa set the goal of reducing non-point source N loads 41%. Implementing winter rye cover crop into agricultural systems is one of the more promising strategies to reduce N loads to subsurface drainage, but its effectiveness in the Mississippi River Basin under expected climate change is uncertain. We used the tested Root Zone Water Quality Model (RZWQM) to estimate N loads to drainage and crop yield in a central Iowa corn-soybean rotation both with and without winter rye cover crop under: 1) observed weather and ambient CO2 (1991–2011, baseline, BL_CC and BL_NCC) and 2) projected future temperature and precipitation change from six Global Circulation Models (GCMs) and elevated CO2 (2065-2085; CC and NCC). Average annual N loads to drainage under NCC, BL_NCC, CC and BL_CC were 64.0, 47.5, 17.1, and 18.9 kg N/ha. N load to drainage was reduced with CC compared to BL_NCC more than 41% for 18 to 21 years depending on the GCM. Under projected climate change, average annual simulated crop yield differences between scenarios with and without winter rye were approximately 0.1 Mg/ha. These results suggest that implementing winter rye cover crop in a corn-soybean rotation effectively addresses the goal of N load reduction to drainage under climate change in a northern Mississippi River Basin agricultural system without affecting cash crop production.