The Effect of Cover Cropping on Potentially Mineralizable Nitrogen.

Continuous corn silage cropping systems in Wisconsin 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 7-day anaerobic incubation (2015 and 2016 season), a long-term aerobic incubation (2015 season), and N uptake by corn. The cropping system was a continuous corn silage system with fall manure application. The experiment was a randomized complete block split-plot design where the whole plot treatments were no cover, rye as a cover (chemically terminated) or as a forage (harvested) crop and the split plot treatment was depth (0-15 cm and 15-30 cm). There were no statistical differences in short-term PMN among cover crop treatments at any time point in the 2015 season. However, the PMN for both the no cover crop and rye forage treatments decreased over the growing season, while the PMN for rye cover did not. There was a reduction in plant N uptake from no cover to rye as cover treatment and from rye as cover to rye as forage treatment. Thus, our study showed significant effects of cover cropping on agronomic factors like corn yield and N uptake but these same differences were not measurable in the soil.