Growing, managing cover crops
Grain producers are learning more about the relationship between the use of cover crops and improved soil health and increased yields.
Planted between harvest and spring, cover crops reduce soil erosion, limit nitrogen leaching, suppress weeds, increase soil organic matter and improve overall soil quality.
Planting small grain cover crops helps cover more surface, keeps corn and soybean residues in place, reduces erosion and increases water infiltration.
Cover crops planted in Iowa include rye and wheat, since they are winter hardy. Less common plants that are still effective include oats, spring wheat, hairy vetch, red clover, sweet clover, turnips, rapeseed, radishes and triticale.
According to the NRCS’ pamphlet, “A Guide for Iowa Producers,” cover crops may reduce total energy demands of the farm by capturing nutrients that would be lost to leaching, thus reducing the farm’s requirement for high energy inputs. NRCS tips for managing cover crops include:
Grasses use more soil nitrogen. Legumes use both nitrogen and phosphorus. Deep-rooted species provide maximum nutrient recovery. Species like rye will produce high volumes of organic matter if allowed to grow longer in the spring.
To maximize weed suppression, leave cover crop residues on the soil surface to maximize allelopathic and mulching effects. Select species that have a large tap root to break up compaction. Mixing two or more species benefits in different ways, since each species performs differently.
Winter hardy grains include cereal rye, winter wheat, triticale (a cross between rye and winter wheat).
Seeding rates are one to two bushels per acre. Winter-killed grains include oats and spring wheat, and seeding rates are two to three bushels per acre.
Winter hardy legumes include hairy vetch, red clover and sweet clover. Seeding rates for those are 8 to 15 pounds per acre.
Forage covers that are winter-killed include turnips, rapeseed and radishes, and seeding rates for those are five to 15 pounds per acre.
Forage covers include turnips, rapeseed and radishes, with a seeding rate of five to 15 pounds per acre.
Each group of cover crops has specific management information and is best used in various ways, so producers should check with their local NRCS office to find what will work best for their needs.
Seeding dates are critical, allowing for adequate growth to provide the intended benefit.
If seeding prior to harvest, seeds can be broadcast via an airplane or high-clearance applicator. No seedbed preparation is necessary. Broadcasting before harvest will require good soil moisture near the ground’s surface.
Seeding after harvest will allow for no-till seeding or broadcasting into existing residue cover.
Immediately roll or cultipack if the seed is broadcast on a prepared seedbed to ensure good seed-to-soil contact. Some producers mix seed in the fertilizer application to reduce the number of passes over the field.
Killing cover crop can be critical for success of the spring-planted crop. Killing them as late as possible will maximize plant growth and residual nutrient accumulation.
Producers should allow time for decomposition, which releases nutrients and recharges soil moisture.
Methods used to kill the cover crop include harvest, crimping, frost, mowing, tillage and/or herbicides compatible with the following crop.
When terminating the cover crop, producers should consider several factors.
Spring termination is not required for cover crops that do not overwinter. They should terminate crops at least two weeks before planting a corn crop to minimize the risk of reducing yields.
Small grains can reduce corn yields similar to continuous corn plantings. Plant chemicals released into the soil can inhibit growth of corn and some weed species.
That’s why the two-week killing period before planting the next crop is important.
Overwintering cover crops should be terminated when they start to regrow, especially if the spring is dry or the long-range forecast predicts dry conditions.
Producers should increase seeding rates for no-till corn by 10 percent when preceded by small grain cover crop.
Increased surface residue can interfere with planter operations and seed placement.
Those thinking about using cover crops should consider using a starter fertilizer containing nitrogen to help microbes decompose organic matter.
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