Surface runoff and nutrient dynamics in cover crop-soybean systems in the Upper Midwest

Authors: Weyers, Sharon; Gesch, Russell - Russ; FORELLA, FRANK - Retired ARS Employee; EBERLE, CARRIE - University Of Wyoming; THOM, MATTHEW - Bergen County Technical Schools; MATTHEES, HEATHER - Land O'Lakes, Inc; OTT, MATTHEW - University Of Minnesota; Feyereisen, Gary; STROCK, JEFFREY - University Of Minnesota

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2020
Publication Date: 1/1/2021
Citation: Weyers, S.L., Gesch, R.W., Forella, F., Eberle, C.A., Thom, M.D., Matthees, H.L., Ott, M., Feyereisen, G.W., Strock, J.S. 2021. Surface runoff and nutrient dynamics in cover crop-soybean systems in the Upper Midwest. Journal of Environmental Quality. 50(1):158-171. https://doi.org/10.1002/jeq2.20135.
DOI: https://doi.org/10.1002/jeq2.20135

Interpretive Summary: Winter hardy cover crops for the Upper Midwest are needed to help reduce nutrient loss in surface runoff. Research conducted at Morris, MN, evaluated the ability of the novel over-wintering oilseed crops, winter camelina and pennycress, to reduce nutrient and sediment loads in runoff water from snowmelt, spring rains and during relay-sown soybean production. Overwintering covers contributed to nutrient load in meltwater in late winter, largely due to their ability to trap snow. However, overwintering oilseed crops were effective at reducing runoff, and nutrient and sediment loads during high impact spring and early soybean growing season rainfall events, compared to fallow systems. These novel winter cropping systems provide a mechanism to reduce potential nutrient loss to surface waters, but also can be harvested, which provides an economic incentive for their adoption. These results will help researchers, land managers and policy makers to develop, support and promote cover cropping strategies that provide both environmental and economic benefits.

Technical Abstract: Relay-cropping of the novel oilseeds winter camelina (Camelina sativa L.) and pennycress (Thlaspi arvense L.) with short-season crops such as soybean [Glycine max (L.) Merr.] can provide economic and environmental incentives for adopting winter cover crop practices in the U.S. Upper Midwest. However, their ability to reduce nutrient loss in surface runoff is unknown. Accordingly, surface runoff and quality were evaluated during three seasonal phases (cover, intercrop, and soybean) over 2 yr in four cover crop–soybean treatments (pennycress, winter camelina, forage radish [Raphanus sativus L.], and winter rye [Secale cereale L.]) compared with no-till and chisel-till fallow treatments. Runoff was collected with Gerlach troughs and assessed for concentrations and loads of NO3-–N, total mineral N, soluble reactive P (SRP), and total suspended solids (TSS). Cumulative runoff and nutrient loads were greater during the winter cover phase because of increased snow melt and freeze–thaw released nutrients from living vegetation. In contrast, cumulative TSS was greater during intercrop and soybean phases due to high-intensity rainfall events with an open soybean canopy. Average TSS loads during the intercrop phase were reduced by 75% in pennycress compared with fallow and radish treatments. During the soybean phase, average TSS, total mineral N, and SRP loads were generally elevated in cover crop treatments compared with no-till. Overwintering cover crops may contribute to mobility of nutrients solubilized from living or decomposing vegetation; however, this was balanced by their potential to reduce runoff and TSS during high-intensity spring rains.