Best management practices to integrate cover crops and manure

Melissa Wilson

There is a growing interest in using cover crops for improving soil health and water quality. In cool, northern climates, however, adoption is low due to the short growing season. On the other hand, interseeding cover crops allows more time for growth and is becoming popular. Liquid manure application, which often happens in the fall in this region, is one practice that could benefit from the use of cover crops. Newer injection technologies have made manure application into cover crops possible, but many questions remain. With a mix of on-farm and small plot research, we studied the effectiveness of a variety of cover crop seeding practices into corn and soybean; fall manure application timing versus spring fertilizer treatments with and without cover crops; soil health characteristics; and the impact of the studied practices on the following corn crop yield.

We found that getting the cover crop planted as early as possible was beneficial for biomass production. Following sweet corn, cover crops could be drilled, but broadcast seeding into soybean around leaf-drop was better than drilling after soybean harvest. When it comes to manure application, we were able to successfully inject manure into the cover crop, though weather conditions seemed to dictate how well the cover crop recovered in the injection zones. As far as application timing, early fall applications when soil temperatures were above 50ºF resulted in a 20 bushel per acre yield reduction compared with spring fertilizer. Waiting until after soils had cooled to below 50ºF resulted in similar or better corn yields than spring fertilizer. This trend happened regardless of whether cover crops were planted or not. In the short time of this study (a two-year period in each field), we did not detect any changes in soil health (pH, bulk density, permanganate oxidizable carbon (POXC)) regardless of the practices used.

Future research should evaluate these practices over the longer-term. Overall, this information will help farmers incorporate cover crops into their production systems when fall manure application is involved. This research also re-iterates that waiting until soil temperatures are cool in the fall to apply swine manure is a best management practice.