Cover crops can add nutrients and help with weed control

by Scott Miller, Clemson University

Dorchester County farmer Jimmy Fender was skeptical, opting reluctantly to skip fertilizer treatments and rely on cover crops for the nutrients that would feed his cash crop.

Fender planted a mix of clover, vetch and radish in September 2014 to serve as winter cover on about 100 acres of cornfield. In late March, he killed the cover and tilled it into the soil, which added an estimated 90 pounds per acre of nitrogen to his field. As part of a trial test with the Natural Resources Conservation Service (NRCS), Fender skipped some fertilizer treatments in part of that field. In the end, yields were close to those where more fertilizer was applied.

“It was hard not to apply fertilizer. It was hard,” Fender said. “But it has convinced me that with a good cover crop, you can get a good yield.”

Fender invited fellow farmers to his property Sept. 1 to view the results of his trial as part of an educational program on cover crops offered by Clemson University Extension and the NRCS. The Dorchester Soil and Water Conservation District sponsored the event.

This year, Fender will plant cover crops on about 200 acres of fields where he plants peanuts and corn. That’s about 17 percent of his family farm.

“We’re just getting started with this,” Fender said.

Cover crops offer several potential benefits. They add nutrients. They also suppress weed growth, reduce erosion and increase soil organic matter content, which helps soil retain water and nutrients.

Clemson Extension agent Rebecca Hellmuth demonstrated the movement of water and nutrients through soil by conducting a “blue dye test.” Blue dye was placed on the soil surface. Hellmuth then applied the equivalent of one inch of water to simulate irrigation. After digging down into the soil profile, the dye could be seen 15 inches deep. Building up organic matter by planting cover crops can help prevent that leaching and retain those nutrients and water in the soil’s root zone.

NRCS agronomist Gordon Mikell said the roots of cover crops also may reduce soil compaction. Roots cannot penetrate soil compacted at 300 pounds per square inch, which is why many farmers till, Mikell said.

“We think these covers can be our tillage tool,” Mikell said.

That would reduce soil disturbance, one of the four keys to healthy soil, said Jeff Lucas, a district conservationist with the NRCS. Tillage actually can compact soil, which is destructive to soil microbes. Disturbance from excess fertilizer can disrupt the relationships between microorganisms and plant roots.

Among the three other keys to healthier soil, NRCS recommends the following:

  • Keep soil covered to conserve moisture, suppress weed growth and provide habitat for soil inhabitants that spend some time above ground.
  • Maintain a living root growing throughout the year to provide food for soil microbes.
  • Use a diverse mix of plants, which supports resistance to insects, disease and drought.

If planting cover crops, farmers should let them grow through March to maximize nutrient content, Lucas said. Farmers can apply with the NRCS for cost-share assistance to plant cover crops, Lucas said.

“Soil health is big for us,” he said.

Fender recommends planting covers such as oats that don’t grow as tall as rye because it is easier to manage. His per-acre seed mix for this test included 10 pounds of vetch, 10 pounds of clover and one pound of radish. The cover crops produced an estimated 90 pounds of nitrogen per acre. Fender applied 70 pounds of nitrogen per acre with chicken litter and 74 pounds of additional commercial nitrogen, less than half of what he would have applied if he had not grown cover crops. To that, he split 64 rows of corn into two test plots. In one, he added a fertilizer “starter.” In the other, he did not. The field without the starter produced 198.3 bushels per acre. The field with starter produced 223 bushels per acre.


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