Organic crop farmers have traditionally relied on cover crops to address a number of resource concerns.
John Lee, agronomist with the Arkansas state office of USDA’s Natural Resources Conservation Service, said they serve multiple functions. “Pest management is one of those, with respect to controlling weeds,” Lee told Ozarks Farm & Neighbor, “but they are also using cover crops to deal with different types of pathogens that are in the soil. There are cover crops that can help reduce some of the disease causing pathogens that you can find in the soil. Also, they can be used as a trap crop to attract beneficial insects, which also help to control pest problems related to insects.”
In Arkansas, Lee said the main crops sown for cover are the grasses used for erosion control; wheat is number one, followed by ryegrass. A number of farmers have also turned to the “tillage radish,” Raphanus sativus, also known as the daikon or the Japanese radish. It has fast-growing leaves and a very large taproot that helps retain soil moisture and breaks up shallow layers of compacted soils. When they break down, they add to the winter stores of nitrogen in the soil.
Those have been the traditional roles of cover crops in organic farm plans, with the crops plowed under as the planting season approaches. However, Kerry Clark, organic row crop specialist at the University of Missouri Bradford Research Farm at Columbia, Mo., said they’re now also being used in organic no-till. She explained to OFN, “In organic no-till, you grow the cover crop until it gets reproductive so it would be fairly large, and then you crimp it with a roller-crimper. The crimper kills the cover crop, but it leaves it on top of the ground as a mulch. It’s usually about 3 to 4 inches thick, and that helps stop the weeds.” Organic matter left on the surface breaks down slower and builds up faster than residue that’s cut or tilled into the soil, so more of it is retained.
Clark said the roller-crimper method was pioneered by Pennsylvania’s Rodale Institute. On the other hand, the Missouri researchers are finding the weeds do eventually come through the cover crop.
“You have to have so much biomass out there in the cover crop that if you don’t have a good growing winter it won’t hold the weeds back,” she said, “The other thing is that as it starts to break down over the season, you’ll also get some later weed germination and growth.” Researchers have begun looking at a number of different approaches to weed control in organic crops. In one, once the cover crop is crimped, a hot water spray is applied. In another, they mow between rows and in a third, they mow and till in the cover crop, and then control weeds through flaming, which is directing a flame below the crop’s leaves toward the weeds, and cultivation.
Clark is working with organic no-till corn, soybeans and wheat and said wheat works the best. The cover crop is grown in the summer instead of double crop beans, and since the soil is left untilled it rapidly increases the organic matter.
“You can’t do organic no-till in front of double crop beans – you wouldn’t have a cover crop to crimp,” she explained. The summer cover crop also provides up to 90 percent weed control. Soybeans get a little more early weed growth than corn because they don’t canopy as quickly, but once they do canopy the weed control is better. However, Clark said she is seeing problems with organic no-till corn. “Because the corn population planting rate is lower than soybeans, it’s hard to get good seed-to-soil contact in organic no-till.” That’s led to reduced stands, but in soybeans and wheat they’ve gotten higher yields in organic no-till than with conventional tillage and no cover crops.
