Nitrate losses in subsurface drainage and nitrous oxide emissions from a winter camelina relay cropping system reveal challenges to sustainable intensification

Authors: Emmett, Bryan; O'Brien, Peter; Malone, Robert - Rob; Rogovska, Natalia; Kovar, John; KOHLER, KEITH - Retired ARS Employee; KASPAR, THOMAS - Retired ARS Employee; MOORMAN, THOMAS - Retired ARS Employee; JAYNES, DAN - Retired ARS Employee; PARKIN, TIMOTHY - Retired ARS Employee

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/2022
Publication Date: 8/18/2022
Citation: Emmett, B.D., O'Brien, P.L., Malone, R.W., Rogovska, N.P., Kovar, J.L., Kohler, K., Kaspar, T.C., Moorman, T.B., Jaynes, D.B., Parkin, T.B. 2022. Nitrate losses in subsurface drainage and nitrous oxide emissions from a winter camelina relay cropping system reveal challenges to sustainable intensification. Agriculture, Ecosystems and Environment. 339. Article 108136. https://doi.org/10.1016/j.agee.2022.108136.
DOI: https://doi.org/10.1016/j.agee.2022.108136

Interpretive Summary: Corn and soybean crops are highly productive in the Upper Midwest. However, these systems can result in nutrient pollution when soils are left bare from late fall through spring allowing nitrogen to move into streams and lakes. Cover crops can be planted after harvest of the main crop, so that they take up leftover nitrogen, and are successful at reducing nitrogen pollution in surface waters. But growing cover crops is also costly to growers. Winter camelina is a winter cash crop that is harvested for the oil in its grain and when grown between corn and soybean it may be able to increase total crop yields and revenue while achieving the environmental benefits of a cover crop. In this study, we compared grain yields, water quality and greenhouse gas emissions of a typical rotation of corn and soybean with a rotation that included winter camelina planted after corn harvest and grown along-side soybean in the early spring. We identified several challenges to achieving economic and environmental goals in the winter camelina system. Corn and soybean grain yields were reduced, water quality was not improved and emissions of nitrous oxide, a strong greenhouse gas, increased because of additional nitrogen fertilizer applied to the camelina. While the results highlight several challenges, the research also points to strategies, such as modifying fertilizer applications, that could reduce the environmental impact of the corn-winter camelina-soybean system. This information will help scientists and growers who are experimenting with winter cash crops grown between corn and soybean continue to improve these systems for both environmental and economic gains.

Technical Abstract: Sustainable intensification strategies seek to increase production while decreasing the environmental footprint of agricultural systems. In the Upper Mississippi River Basin, relay cropping of a winter oilseed crop between corn and soybean has gained interest for its potential to increase total yields and revenue while providing the environmental benefits of winter cover. In a six-year field study in central Iowa, a basic corn-soybean rotation was compared with a corn-winter camelina-soybean relay cropping system for crop yields, nitrate losses in drainage and nitrous oxide emissions from soil. Corn and soybean yields were decreased in the relay cropping system by 9.8% and 23.3%, respectively, as a result of management changes to the system and interspecific competition. However, combined grain dry weight of soybean and the camelina oilseed crop were similar to the soybean yield in the basic corn-soybean rotation. Despite filling a niche as an overwintering crop with the potential to assimilate soil nitrogen, nitrate loads in drainage were not reduced in the camelina relay cropping system. Management changes to support the camelina crop tripled cumulative N2O emissions during the camelina-soybean phase over the course of the study, from 3.57 kg N2O-N ha-1 in the basic corn-soybean rotation to 12.2 kg N2O-N ha-1 in the camelina relay system. Most of the increased emissions in the camelina system were associated with peak emissions events following tillage and starter fertilizer application in the fall and during the spring thaw, which may point to risks of exacerbating greenhouse gas emissions during fall management of a relay crop. These findings highlight the need for careful evaluation and optimization of sustainable intensification systems to ensure environmental and production goals are met.