Soil nitrogen in response to interseeded cover crops in maize-soybean production systems

Authors: Mohammed, Yesuf; PATEL, SWETABH - Iowa State University; MATTHEES, HEATHER - Winfield Solutions; LENSSEN, ANDREW - Iowa State University; JOHNSON, BURTON - North Dakota State University; WELLS, M - University Of Minnesota; FORCELLA, FRANK - Retired ARS Employee; BERTI, MARISOL - North Dakota State University; Gesch, Russell - Russ

Submitted to: Agronomy
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/14/2020
Publication Date: 9/22/2020
Citation: Mohammed, Y.A., Patel, S., Matthees, H.L., Lenssen, A.W., Johnson, B.L., Wells, M.S., Forcella, F., Berti, M.T., Gesch, R.W. 2020. Soil nitrogen in response to interseeded cover crops in maize-soybean production systems. Agronomy. 10(9). Article 1439. https://doi.org/10.3390/agronomy10091439.
DOI: https://doi.org/10.3390/agronomy10091439

Interpretive Summary: Current corn and soybean production practices in the upper Midwest are resulting in nutrient losses and limited plant diversity. Nutrient losses are economic losses to growers and cause water pollution as well. To minimize these losses and increase plant diversity, we evaluated three interseeding dates and cover crops (winter rye, pennycress and winter camelina) on carbon and nitrogen accumulation in the biomass and impact on soil mineral nitrogen (ammonium and nitrate). The cover crops were interseeded in standing corn and soybean at three reproductive stages of corn and soybean. The results showed that winter rye decreased soil nitrate by 76% compared with no-cover crop treatment. Pennycress at Prosper (North Dakota) and winter camelina at Morris (Minnesota) also showed potential to lower soil nitrate; thus, adoption may lead to improved water quality and increased plant diversity. The effects of interseeding date on cover crops biomass carbon and nitrogen accumulation was minimal thus may allow growers to have flexible time for interseeding cover crops. Winter rye generally had greater potential to accumulate carbon and nitrogen, which could improve nutrient cycling within the system. The decrease in soil nitrate due winter camelina at Morris and pennycress at Prosper was comparable with winter rye indicting the importance of site-specific adoption of oilseeds. Generally, pennycress and winter camelina showed lower carbon accumulation in the shoots than winter rye. Therefore, we suggest developing improved varieties of these oilseeds that can perform better when interseeded in standing corn and soybean. In addition, valuing pennycress and winter camelina ecosystem services and assessing agronomic practices other than interseeding are needed strategies to enhance crop diversification, improve water quality and nutrient cycling. This information will benefit producers interested in growing cover crops, extension specialists and consultants in advising producers. The information will also benefit other scientists interested in developing best management practices for interseeding cover crops to reduce soil nitrate and enhance crop diversity in the corn and soybean production systems.

Technical Abstract: Improved agronomic management strategies are needed to minimize the impact that current maize (Zea mays L.) and soybean (Glycine max (L.) Merr.) production practices have on soil erosion and nutrient losses, especially nitrogen (N). Interseeded cover crops in standing maize and soybean scavenge excess soil N and thus reduce potential N leaching and runoff. The objectives were to determine the impact that pennycress (Thlaspi arvense L.) (PC), winter camelina (Camelina sativa (L.) Crantz) (WC), and winter rye (Secale cereale L.) (WR) cover crops have on soil N, and carbon (C) and N accumulation in cover-crop biomass. The cover crops were interseeded in maize at the R5 growth stage and in soybean at R7 in four replicates over two growing seasons at four locations. Soil and aboveground biomass samples were taken in autumn and spring. Data from the maize and soybean systems were analyzed separately. The results showed that cover crops had no effect on soil NH4+-N under both systems. However, winter rye decreased soil NO3--N up to 76% compared with no-cover-crop treatment in the soybean system. Pennycress and WC scavenged less soil N than WR. Similarly, N and C accumulation in PC and WC biomass were less than in WR, in part because of their poor growth performance under the interseeding practice. Until PC and WC varieties with improved suitability for interseeding are developed, other agronomic practices may need to be explored for improving N scavenging in maize and soybean cropping systems to reduce nutrient leaching and enhance crop diversification.