Short-Term Benefits of Cover Crops on Labile Carbon and Nitrogen Pools in Soil.

Continuous corn silage cropping systems lead to overall removal of N from the system, unless manure is applied. However, this cropping system allows for the planting of cover crops or a winter silage crop post harvest, which may lead to increases in soil N over time. Cover crops are valuable in these corn-silage based rotations as they also provide ground cover after harvest and can reduce N leaching after fall manure application. The objective of this study was to determine the effect of cover cropping on potentially mineralizable nitrogen (PMN) over a growing season using a short-term anaerobic incubation, a long-term aerobic incubation, and permanganate oxidizable carbon (POXC) in a continuous corn silage production system. Three treatments were established in 2011: no cover crop, rye as a cover crop, and rye as a forage crop (harvested). Rye, as a cover and as a forage, had greater PMN throughout most of the growing season in 2016. However, there were no statistical differences in short-term PMN among cover crop treatments at any time point in the 2015 season. Despite being strongly correlated with 7d-PMN, our POXC results did not show the same effect of cover crops as 7d-PMN did. The results from the long-term incubation indicates that these soils maintained a consistent rate of mineralization across 40 weeks. Kinetic models, widely used to determine N mineralization potential, do not appear to be appropriate estimates of N mineralization on these manured soils. Overall, different measures of labile C and N pools differed in their sensitivity to cover crop management, but based on 7d-PMN, continual cover crop use can lead to increases in N mineralization.