By Jonathan Eisenthal
Cover crops and manure are tools that help farmers keep soil in place and provide nutrients for row crops. University of Minnesota Extension Associate Professor Melissa Wilson has spent three growing seasons looking at the best ways to use these tools together. There have been two basic findings: the earlier the cover crop is planted, the more biomass it will produce, and with fall placement of manure, later is better than early.
Her work, funded by the Minnesota Corn Research & Promotion Council, focused on timing of liquid manure placement, along with a variety of cover crops mixes. The combination of the two practices was examined in several rotations: sweet corn followed by field corn and soybeans followed by corn. As controls, her team also included plots where no cover crops were planted and where fertilizer was used instead of manure. The project utilized plots both on experiment station land and working farms.
Wilson said her team had more success with cover crops following sweet corn, because they were able to drill the cover crop early in August. Compared to drilling the seed in late summer, broadcasting between the rows of standing crops didn’t produce as much biomass. Wilson attributes this to less soil-to-seed contact.
On farm plots
The on-farm plots demonstrated that cover crops and manure can work well together, and they also demonstrated that terminating the cover crop before planting the cash crop leads to better yields than planting into living cover crops.
In both cases, the farmers used strip-till cultivation. One farmer tested fall placement of manure versus fall placement of fertilizer, and the other farmer only tested manure. Both farmers tested the timing of terminating the cover crop.
Yields were similar regardless of the nutrient source, but they did decline slightly when the cover crop was allowed to stay on the field later into the spring.
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