Saving time and saving dollars are the major reasons cover crops have worked so well in no-till rotations for many Virginia growers.
Grow Own Nitrogen
Paul Davis is convinced he’ll eventually be able to meet all of his corn-crop nitrogen needs from the cover crops he seeds each fall. The New Kent, Va., no-tiller has been using cover crops for 6 years, and relied on cereal rye for several years before switching to hairy vetch on much of his acreage.
“One concern may be that the nitrogen from the cover crops may not be available early enough in the cropping season,” he says. “But I think we could still utilize all of the available nitrogen from our cover crops by the time we sidedress corn.”
Davis obtains 60 to 80 pounds of nitrogen from the hairy-vetch cover crop, applies 40 to 50 pounds of nitrogen in starter fertilizer and sidedresses another 60 pounds of nitrogen to harvest 200-bushel corn yields. By no-tilling hairy vetch after full-season soybeans, Davis has dropped nitrogen sidedressing needs with corn from 120 pounds per acre to only 60 pounds.
“We don’t yet have a good answer as to how many pounds of nitrogen we need after a cover crop,” says Davis. “We tissue-test corn plants, along with the amount of biomass in the soil, to determine the precise amount of nitrogen needed for sidedressing. Our goal is to rely on the cover crop to boost soil organic matter and sequester carbon.”
Sense Nitrogen Needs
Davis has worked extensively with a Greenseeker plant-sensing unit to use nitrogen more efficiently. He credits the technology with trimming his nitrogen costs by 15% on corn, and 10% with no-tilled wheat. He finds the nitrogen-sensing system works best when corn is 18 to 36 inches tall.
“The greener the leaf, the more red color is reflected up into the six Greenseeker units installed on our spray boom,” he says. “We run the boom 35 to 40 inches above the top of the corn at 15 mph.
“In 5 years, I think all the big-acrege growers will have one. Once nitrogen prices spike upward, it will have an impact on this technology. This is practicing nutrient management right in the field.”
Rye Works Best
Wade Thompson, a Virginia Tech agronomist, found rye produced the best results in cover crop trials with oats, hairy vetch, barley, rye, triticale and wheat. Rye provides nitrogen for corn, increases soil organic matter and builds carbon.
“There’s some risk with hairy vetch,” he says. “Sometimes you only get half as much nitrogen as usual due to the extremely dry conditions that occur in March and April here in Virginia.”
Thompson maintains cover crops can dramatically improve carbon sequestration. “Without cover crops, you’ll maximize your carbon sequestration in 15 years,” he says. “By seeding cover crops, you can extend this period to over 35 years.”