Productivity of Cover Crops and Primary Crops in Nebraska Corn-Soybean Systems.

High biomass production is crucial for the delivery of cover crop (CC) ecosystem services such as sequestering soil organic carbon, preventing soil erosion and nutrient loss. In Nebraska, winter CC productivity in corn and soybean systems is limited by growing season length and available soil moisture. Further, CC productivity might be higher preceding soybean than corn, since soybean is typically planted later than corn, extending cover crop growth in the spring. Cover crop growth in the fall can be extended by planting into corn and soybean stands before these crops reach maturity.

Our objectives were to assess CC and related primary crop productivity in corn-soybean systems at four sites along the temperature and precipitation gradient across Nebraska. Cover crops included cereal rye, forage radish,  hairy vetch and winter pea, and a mix which were either broadcast into corn and soybean stands when corn was at half-milk (early planting) or drilled after corn or soybean harvest (late planting).

More CC emerged in late (drilled) than the early (broadcast) treatment, but CC species and planting times also interacted with cropping system. Spring biomass was higher in the broadcast treatment and highest in CC planted before soybeans as this cropping system allows for longer CC growth in the spring. Rye produced the most biomass in 2016, up to 4500 lb/A at the north-east site. Hairy vetch and winter pea produced less than 400 lb/A. The mix was intermediate in biomass yield. The site in Western Nebraska produced the least biomass. Reductions in 2016 corn and soybean yields were observed after rye at some sites.

Rye was the only species to consistently produce biomass in corn-soybean systems in Nebraska. Rye was also the predominant component of the mix. High CC productivity can impact primary crop yields, lead to soil moisture deficits and potential benefits of cover cropping must be weighed against potential primary crop yield losses.