Environmental trade-offs of relay-cropping winter cover crops with soybean in a maize-soybean system

Authors: CECCHIN, ANDREA - North Dakota State University; POURHASHEM, GHASIDEH - North Dakota State University; Gesch, Russell - Russ; LENSSEN, ANDREW - Iowa State University; Mohammed, Yesuf; PATEL, SWETABH - Iowa State University; BERTI, MARISOL - North Dakota State University

Submitted to: Agricultural Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2021
Publication Date: 1/21/2021
Citation: Cecchin, A., Pourhashem, G., Gesch, R.W., Lenssen, A.W., Mohammed, Y.A., Patel, S., Berti, M.T. 2021. Environmental trade-offs of relay-cropping winter cover crops with soybean in a maize-soybean system. Agricultural Systems. 189. Article 103062. https://doi.org/10.1016/j.agsy.2021.103062.
DOI: https://doi.org/10.1016/j.agsy.2021.103062

Interpretive Summary: Winter camelina and field pennycress are two winter annual oilseeds that can serve as both cash and cover crops. Establishing these oilseeds as covers in a corn-soybean system has been challenging because corn is generally harvested too late in the fall to directly plant cover crops before the soil freezes. In this study, winter camelina, pennycress, and winter rye were interseeded into standing corn during late summer/early fall and the following spring soybean was relay cropped. An environmental impact assessment of this system was then conducted using a life cycle assessment approach (LCA). On an area per year basis, when winter oilseed cover crops were used in the cropping system and not given any nitrogen fertilizer, the system had lower water pollution potential and soil erosion, and lower global warming potential (GWP) than a business as usual corn-soybean rotation. However, on an economic basis, camelina and pennycress did not work as well in the interseeding system. The two primary reasons for this were: 1) the added costs for establishing the oilseed covers including nitrogen fertilization, and 2) relatively poor yields of both the winter oilseeds and relayed soybean associated with the interseeding system and methodology used. This information is valuable to researchers and agricultural extension specialists who are focused on developing better management practices for establishing cover crops in the traditional corn-soybean rotation used in the US Corn Belt.

Technical Abstract: Winter camelina [Camelina sativa (L.) Crantz] (Cam) and field pennycress [Thlaspi arvense L.] (Pen) are oilseed feedstocks that can be employed as winter cover crops in the current cropping systems in the U.S. Upper Midwest. In addition, they can provide a further source of income for the farmer. However, using Cam and Pen as winter cover crops is a new agricultural practice that has only been studied recently. The objective of this study was to assess and compare the environmental performance of a relay-cropped maize [Zea mays L.]-soybean [Glycine max (L.) Merr.] with different winter cover crops - Cam, Pen, and winter rye (Secale cereale L.) (Rye) - in the U.S. Upper Midwest. The field experiments were carried out from 2016 to 2017 (two-year maize-soybean rotation) in three locations in the U.S. Upper Midwest: Morris (Minnesota), Ames (Iowa), and Prosper (North Dakota). The environmental impact assessment was carried out using a "cradle-to-gate" life cycle assessment (LCA) methodology. Two functional units (FU) were selected: (1) 1 ha year-1 (land-based FU), and (2) $1 net margin (economic FU). When expressed with the FU ha yr-1, cover crops had (a) lower eutrophication potential and water soil erosion, and (b) lower global warming potential (GWP) if the cover crop was not fertilized with nitrogen. Winter camelina and Pen were more effective than Rye in reducing soil losses, while the three cover crops provided similar results for eutrophication potential. When expressed with the FU $ net margin, Cam and Pen were overall the worst sequences in mitigating greenhouse gases (GHGs) emissions, and nutrient and soil losses. This performance was mainly due to the seed yield reduction of both the main cash crop (soybean) and the cover crop on relay compared with the conventional sequence maize-soybean. The results of this study suggest that the introduction of Cam and Pen as winter-hardy cover crops has a strong potential for reducing the environmental impacts of the maize-soybean rotation in the U.S. Upper Midwest. However, a better field management of nitrogen fertilization and crop residues of these cover crops in a relay-cropping system is needed to make them a viable and sustainable agricultural practice.