By Jochum Wiersma
Establishing cover crops in corn and soybeans is not without its challenges in Minnesota. There is little growing season left after harvest and soil moisture and herbicide carryover can often limit the ability to get a good cover crop stand when interseeding mid-season. In response to these growing season limitations, new interseeding technologies offer the promise to overcome some of the establishment issues in Minnesota (click here
for more information). Even with the most advanced interseeding technologies, cover crop establishment success will be greater following short season crops. Wheat, barley, and oats make establishing cover crops much easier. There is plenty of growing season left following small grain harvest for reliable cover crop establishment. Oftentimes cover crops seeded following small grains accumulate enough biomass to be grazed or harvested for forage in the fall.
Small grains also provide the opportunity to interseed cover crops. After all, interseeding alfalfa with oats is a common method to establish alfalfa. This approach can easily be extended to other legumes, including clovers and even grasses like annual ryegrass. A common practice in NW Europe is to spread annual ryegrass with a fertilizer spreader over the top of winter wheat in early spring. This strategy tends to work well for annual ryegrass and other species that require shallow seeding and light to stimulate germination. This strategy can probably be used successfully to interseed cover crops into wheat, barley, or oats in Minnesota.
The biggest challenges when interseeding legumes in small grains is effective weed control, as many legume species are quite sensitive to the commonly used broadleaf herbicides. It is also important to select the proper legume species to avoid crop competition and harvest difficulty. Legumes like hairy vetch become very competitive when the small grain starts to mature, even to the point where plants impede harvest by reaching the top of the small grain canopy prior to harvest. Alfalfa and red clover are more appropriate choices to interseed with small grains, as UMN research has found they do not impede grain harvest and do not negatively affect hard red spring wheat yield. Other agronomic practices, including fertility management and seeding rates, can remain the same for interseeding small grains when compared to the practices for monocultures of wheat, barley, or oats. More information on previous UMN research on intercropping alfalfa, red clover, and hairy vetch in hard red spring wheat can be found here