Cover crop rotations affect greenhouse gas emissions and crop production in Illinois, USA

Abstract

Nitrogen (N) is an essential element and usually a limiting factor in corn (Zea mays, L.) production; yet N build-up in the soil might lead to nitrate (N-NO3) leaching, and release of nitrous oxide (N2O) by denitrification, thus contributing to both water and air pollution. Cover crops (CCs) have been used to scavenge surplus soil N, which might lead to a decrease in the substrate needed for N2O production from the field. The objective of this study was to determine the effect that corn-soybean rotations with different CCs, and tillage methods have on greenhouse gas (GHG) emissions and crop yields in Illinois, USA. The experimental design was a split-block arrangement of tillage (chisel vs. no-till) and CC rotations in a RCBD with 4 replications with the corn and soybean [Glycine max (L.) Merr.] phases present each year. Greenhouse gas emissions - nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) – soil available N, (NO3 and NH4) were sampled only during the actively growing cover crop period and from the corn phase of each rotation over a period of 4 years (2013–2017). Cover crop rotations included five corn-soybean rotations with different CCs and one with an unseeded control. Our results suggest that CC efficacy in a humid continental climate, like central Illinois, is associated with fall and winter temperature and precipitation. In two of the years, spring CC growth was poor due to unseasonably cold temperatures; however, in two of the other years, weather was favorable and spring CC biomass ranged from 2-3 Mg ha−1 from three of the species tested. Where spring CC biomass was measurable, a fivefold reduction in N2O emissions was associated to significant reductions in soil N-NO3. Corn yields were not improved with the utilization of CCs and a yield decrease of 12% occurred in the annual ryegrass (Lolium multiflorum Lam.) rotation. The findings from this study are the first from Illinois and one of few from the Midwest showing the potential benefits CCs have in reducing GHG emissions. Moreover, given adequate growing conditions, some CC species can significantly reduce GHG emissions, decrease residual soil N, and have no negative effects on cash crop yields.