Talkin’ cover crops
Turning whole fields into buffer strips
September 19, 2010 - By LARRY KERSHNER, For the Messenger
WEBSTER CITY - Watching an airplane that traditionally is used to spray row crops during the summer, more than 50 people, consisting of grain growers, agribusinesses and farming organizations, gathered north of Webster City Tuesday to watch a demonstration of aerial seeding of winter rye in a cornfield that was yet to be harvested.
The field day, sponsored jointly by Practical Farmers of Iowa, Iowa State University Extension, Iowa Learning Farms and the Natural Resources and Conservation Service was focused primarily on planting small grain cover crops during the fall.
On hand were producers who were using cover crops as a land management tool, plus NRCS personnel to talk about government cost share funds to encourage growers in this region to try using cover crops to reduce erosion, capture nitrogen from leaching away during late-fall and early-spring rains, and to add organic matter to the soil profile.
"Cover crops basically turn the whole field into a buffer strip," said Bruce Voigts, president of the Mississippi River Basin Initiative. Holding a milk carton with sprouting winter rye he described the government funds available as well as the benefits of planting a cover crop just ahead of harvest time, whether from the air or with a seed drill following the combine.
A study completed in 2005 by the U.S. Department of Agriculture - Ag Research Service, noted that "Nitrogen remaining in the soil after harvest is a significant source of nitrate contamination for groundwater, wells, streams and lakes.
"During the late fall and early spring small grain cover crops accumulate nitrates that would otherwise leach out."
Researchers, who tested this study for three years in Iowa, determined that rye, over-seeded into no-till soybeans reduced interrill erosion by 54 percent and rill erosion by 90 percent. Oats reduced interrill and rill erosion by 26 and 54 percent, respectively.
Interrill erosion is when raindrops strike exposed soil detaching the soil particles, splashing them into the air and into shallow overland flows. Rill erosion is the removal of soil by runoff from the land surface.
When the cover crops are killed in the spring ahead of planting, the captured nitrate is returned to the soil by plant residue.
"Small grain cover crops," the study added, "can reduce the number of early-season weeds and provide mulch for continued weed suppression."
Voigts and others recommended seeding cover crops in corn, just ahead of harvest, and in soybeans as leaves turn yellow. With the seed on the ground, the falling soybean leaves will protect them until germination.
Now in his second year of experimenting with cover crops, Arliss Nielsen, of Woolstock, said he is still learning how to use small grains to benefit his soil but said the earlier the grains can be seeded "the more sunlight they'll get to get established."
Where aerial applications will require about 90 pounds of seeds per acre, or about 1.3 million seeds, drilling small grains following the combine will be successful at a rate of 50 pounds per acre.
But Nielsen believes that as busy as producers are with hundreds and even thousands of acres to harvest, most will likely opt for aerial seeding "just to get it done."
He told Farm News that he is seeing a gradual increase in his yields as he adopts more land management practices and moves away from conventional tillage.
"We're assuming these tests are beneficial," he said. "We're using several practices like no-till, cover crops, variable rate fertilization, increased plant populations. We can't distinguish any one practice. They are all helping."
He said he started seeding small grains using Environmental Quality Incentive Funds from NRCS. He said he wasn't sure how it would work out. "But you never know what will happen until you try it.
"We're learning and we think we are heading in the right direction."
Spring management of cover crops is essential, PFI's Carlson said, because after benefitting from capturing nitrates in the plants and reducing erosion, if the small grains are not destroyed in time, they will become as weeds pressuring corn and soybeans and reducing yields.
Cover crops can be grazed, or chopped as silage or killed by spraying.
The USDA-ARS study determined that by planting oats, which won't overwinter, yield reduction is minimized. Another method is to kill small grains shortly after they start coming up in the spring.
Chemical and mechanical means can be used, Carlson said, but added that machinery can vary in the effectiveness of eliminating the cover.
Contact Larry Kershner at (515) 573-2141, Ext. 453 or at firstname.lastname@example.org.