By Lynn Betts
Let's go straight to the bottom line: "No one species can deliver all the advantages multiple cover crops deliver in combination," says David Lamm of the USDA Natural Resources Conservation Service.
That's why most farmers who start with single species cover crops eventually move to mixes. "Some fix nitrogen. Some are very good at scavenging leftover nitrogen in the soil. Some have deep roots that extend benefits deeper into the soil profile. Still others help control specific weeds or attract beneficial insects," adds this leader for the NRCS National Soil Health and Sustainability Team at Greensboro, N.C.
The value of cover crops isn't in the biomass produced above ground. Rather, it's in the diversity of plant roots that create underground habitat with a healthy balance of predator and prey organisms. That balance improves nutrient cycling and puts organic matter production on the fast track, he declares.
Cocktail mixes pay, even in drought
Jay Fuhrer, a district conservationist with NRCS in Burleigh County, N,D., discovered exactly that while working with several dozen farmers using cover crop mixes. One of his clients bumped their organic matter levels from as low as 1.7 to as high as 5.0.
"Using one or two species is a step in the right direction," says Fuhrer. "But you get more benefits from using several cover crops together. The benefits are exponential with the synergy you create to feed the soil biology with a dozen species together. You can actually accelerate biological time in nutrient cycling."
Fuhrer says first-time cover crop users tend to use only one or two species because they think that's simplest. "A multiple-species planting is actually easier and safer to manage than a single species cover crop," he argues. "The more diversity you have, the more soil biology balance you have below ground."