Influence of gypsum and cover crop on greenhouse gas emissions in soybean cropping systems

Agriculture has the opportunity to mitigate anthropogenic contributions to global change by increasing soil sequestration of greenhouse gases (GHG) and by reducing efflux through management. Common agricultural management practices include crop rotation and use of cover crops. Interest in the use of gypsum in agricultural systems has also increased in recent years. However, little is known regarding how combining gypsum with other management practices impact GHG emissions in soybean (Glycine max [L.] Merr.)-based cropping systems. A study was implemented at three locations (i.e., east-central Indiana, northwest Ohio, and east-central Alabama) to evaluate the influence of gypsum and cover cropping within a continuous soybean and a corn (Zea mays L.)–soybean rotation on crop yield and soil properties. Within this study, carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) were also monitored periodically following soybean seeding through harvest from 2012 to 2016. The combined gas data were then used to calculate a global warming potential (GWP). Overall, few differences in GHG emissions were observed across sites and years, and no consistent patterns were noted, likely due to large variabilities in gas efflux measurements and limited influence of treatments on trace gases. However, treatment differences were observed for one or more GHG within specific years and at specific sites. Comparison across sites revealed the warmer/wetter climate in Alabama resulted in greater CO2 efflux, while climate and soil factors at the northern sites led to greater N2O efflux. At all locations, CH4 emissions were generally low and sites tended to be small net sinks. Given that GHG emissions drive GWP, it also showed few treatment responses and no consistent patterns. It can be concluded from this study that contributions of gypsum and cover crop to GHG emissions from soil in soybean cropping systems will likely have little influence on contributions to global climate change.