Cover crops shield soil in storms
The recent mid-April storm reminded many southern Iowa farmers why there is never a good time for tillage — even after a dry winter and the warmest March on record. Up to 8 inches of rain, along with strong winds and tornadoes, hit southern Iowa on April 14, causing property and cropland damage. In many cases, crop inputs like corn seed and fertilizer washed away.
In Montgomery County, district conservationist Tom Burkhiser, with USDA’s Natural Resources Conservation Service, says a 20,000-acre area with mostly unprotected fields sustained soil losses in excess of 20 tons per acre. Alan Lange, NRCS district conservationist in Adair County, reported similar damage there. He says approximately 25,000 cropland acres lost more than 20 tons of soil per acre.
• Cover crops protect soil from heavy rains on farm fields.
• Combining other conservation practices with cover crops controls erosion.
• Fibrous root systems that cover crops provide also help hold soil in place.
Burkhiser says a definite difference exists in the amount of erosion between tilled and untilled fields. “In fields where tillage was done, sheet and rill erosion is severe,” he adds. “Cornstalks and bean stubble from fields left undisturbed protected the soil well. The biggest problem from this storm is ephemeral gully erosion.”
Heavy rain protection
Farmers like Steve Berger of Wellman in Washington County, who planted cover crops in the fall, went mostly unscathed. Berger says 3 inches of rain fell that evening on his farm. When the sun came up the next morning, however, the cereal rye cover crop that he sprayed with a kill-shot just two weeks prior protected the soil from erosion.
Berger is a 30-year no-tiller. He added a cereal rye cover crop to his rotation 10 years ago. “Cover crops help to reduce soil loss and improve soil health,” he says. “A lot of ground in the area has been worked up as corn is planted, so there were several worked fields with significant soil erosion.”
Typically, it takes more than one conservation practice to protect the soil during heavy rains, especially when heavy rains hit like they did April 14, says Barb Stewart, state agronomist for NRCS in Des Moines. Crop residue management practices like no-till, along with erosion control practices such as terraces, contour buffer strips and grassed waterways, provide good protection against soil erosion.
She says optimal erosion control can be attained by combining those practices with cover crops.
“Cover crops supply another blanket of protection against the impact of raindrops,” emphasizes Stewart, “and cover crop roots help hold the soil in place.”
Pete Hobson, who no-till farms in Pottawattamie County, grew a ryegrass cover crop in corn residue last fall and just recently sprayed it in preparation for planting. He says those fields are free of erosion following more than 3 inches of rain on April 14 and more than an inch a week prior.
What’s soil worth to you?
Hobson benefited most from drilling wheat into a field with soybean stubble in areas most susceptible to ephemeral gullies. “I sprayed the wheat with Roundup the Monday before, and it still kept those gully-prone areas from washing,” he says. “For me, it’s less about the cover and more about the fibrous root systems that cover crops provide that help hold the soil in place.”
During heavy rains, cover crops provide an unintended benefit: keeping crop residue out of culverts. “We saw some problems with cornstalks and bean stubble plugging culverts,” says Burkhiser. “Having cover crops on fields avoids that problem.”
After months of below-average rainfall, many farmers were dealing with saturated fields from the weekend storm. Stewart says cover crops can help in the drying process of fields.
“Cover crop roots provide good soil structure, which allows water to infiltrate,” he says. “Tilled soil leaves you with a muddy mess following heavy rains. It takes a long time to dry those fields out, and leaves you with a hard crust on top.”
“It really comes down to, ‘What is the soil worth to you?’ ” says Stewart. “Is the cost of planting a cover crop worth keeping the soil on your farm?”
Johnson writes for NRCS in Iowa.
COVERED: Crystal-clear water runs off Steve Berger’s cropland after 3 inches of rain fell the night before. The newly sprayed cereal rye cover crop, combined with no-till, helped keep the soil in place. Photo by Steve Berger
WASHING away: As much as 7 inches of rain fell in sections of Montgomery County in southwest Iowa the evening of April 14. Ephemeral gully erosion and sheet and rill erosion (pictured) were widespread.
This article published in the May, 2012 edition of WALLACES FARMER.
All rights reserved. Copyright Farm Progress Cos. 2012.