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Planting cover crops in a drought year can harvest large amounts of residual N and help jump start next year’s crops, according to experts appearing on a webinar Monday. The session, “Dealing with Drought: Securing Nitrogen with Cover Crops,” was hosted by the CropLife Media Group.
“In our experience cover crops offer a great opportunity in a drought year,” said John Meisinger, a USDA soil scientist. Meisinger cited long-term studies in which cover crops significantly reduced N loss and improved soil organic matter.
Keys to conserving residual N with cover crops are early planting and choosing the right plant species.Meisinger cited research in which N uptake by a rye cover crop was 160 lb/ac when planted on October 1, compared with 60 lb/ac when the crop was planted on October 30.
Cereal rye and annual ryegrass were the most successful cover crops in soaking up residual N in Maryland research comparing four different species. Cereal rye recovered about 50% of residual N, he said. “Annual ryegrass also did very nice job.” he said.
Meisinger also touted the long-term benefits of cover crops for building soils. “Soils are made to grow crops, and crops are made to grow soils,” he said.
HOW BEST TO PLANT COVER CROPS
Tom Kaspar, a USDA plant pathologist based in Iowa, pointed to a nine-year study in which a rye cover crop reduced nitrate-N losses by 53% in a corn-soybean rotation.
An important consideration for farmers this year is how to get cover crops seeded. For establishing small grain cover crops, aerial overseeding can be done in corn, just prior to black layer or with soybeans at the beginning of leaf yellow.
“Watch crop maturity, soil moisture, rainfall and temperatures,” he said. “Adjust timing based on latitude.” If you plant later, after harvest, you’ll have the advantage of a lower seeding rate, and more reliable stand establishment. In selecting a cover crop you should consider whether the crop overwinters, how you’re going to establish it and the cost of the seed.
For a seed selection guide, Kaspar pointed webinar attendees to the Midwest Cover Crops Council website, which hosts a Cover Crop Decision Tool (http://www.mcc.msu.edu/).
He also cited the Midwest Cover Crops Fields Guide: http://www3.ag.purude.edu/agry/dtc/Pages/CoverCropsFG.aspx.
In managing the small grain cover crops in the spring, you need to watch soil water levels, rainfall and cover crop growth, Kaspar said. “Before planting corn, kill the cover crop 14 days prior to planting or as soon as the rye is six to eight inches tall. Before soybeans your biggest concern is dry conditions. Otherwise the cover crop can be sprayed up to three days before planting.”
Dave Robison, a forage and cover crop agronomist with Legacy Seeds, focused on the pros and cons of the various N “scavengers,” including brassicas, cereal grains, annual ryegrass, and combinations of cover crops.
Detailed discussion of the advantages and disadvantages of the crops are presented on his blog: http://www.plantcovercrops.com.
He gave cost estimates for the various crops, including winter cereal rye, oats, and annual ryegrass (all $14-$17/ac), cover crop radish ($15-$24) and combinations like a oats, rye and turnip mix ($32-$35/ac).
Aerial application rates in Midwestern states are $15-$18/ac, he said.
Robison encouraged producers to give cover crops a close look in a drought year, despite the challenges of getting a crop established in dry soils. “It’s August 20. Have patience. Be careful to do it right. If I’m going to plant a cover crop now, I’d drill it in, or broadcast and till it in. Maybe pack it, too. Get good soil to seed contact,” he said.
“Even where it’s been dry, we have three to four weeks when we can still get cover crops established over a broad part of the country," Robison said. "But certainly by Labor Day it time to start making some decisions.”