Virginia cotton farmers may want to consider cover crops as one way to add nitrogen and improve soil fertility.

Speaking at the annual Virginia cotton production meeting at the Paul D. Camp Community College Work Force Center in Franklin, Virginia Tech Extension Cotton Specialist Dr. Hunter Frame presented research results showing the fertility benefits of cover crops to cotton.

“Cover crops are known for the soil health benefits, but I’m looking at it from a fertility perspective because we have cheap nitrogen now. I don’t know how long it’s going to be cheap, and one way we could change our cotton systems is to maybe not rely on inorganic nitrogen fertilizer,” Frame said.

Frame and his colleagues are looking at how tillage radishes, high biomass rye cover crops and high biomass legume cover crops affect the nutrient cycle of cotton in-season. Frame noted that high biomass ryes offer a good mulch and help with weed control. For legumes, the research is looking at hairy vetch and crimson clover which are a good nitrogen fixers.

Frame said the rye creates about 5,000 pounds of dry biomass per acre. When the legumes hairy vetch and crimson clover are added, the biomass level is bumped up a bit.

For rye only, Frame and his team drilled 75 pounds of rye seed to the acre. For the legume mix, they applied 15 pounds of hairy vetch and 15 pounds of crimson clover per acre. For the rye-legume mix, they applied 50 pounds of cereal rye seed, 12.5 pounds of hairy vetch seed and 12.5 pounds of crimson clover seed per acre.

The research shows rye alone added about 60 pounds of nitrogen to the above ground biomass. When legumes were added, anywhere from 170 to 180 pounds of nitrogen per acre were found in the above ground biomass.

The research is also looking at potash applications since potash fertility remains a big issue for cotton. In the rye alone system, more than 120 pounds of potash was available in the above ground biomass. “That should be readily plant available when the plant tissue starts to break down after termination,” Frame explained.

When the legume mix was added, Frame said more than 200 pounds of potash were mined and brought up to the above ground biomass. When the biomass starts to decay, the potash should be readily available to the cotton crop.

In the research, cotton planted behind the legume cover crop yielded an average of 1,400 pounds of lint per acre with zero nitrogen applied behind the legume cover crop. However, when nitrogen was added at 90 pound per acre behind the legume cover crop, yields were 1,700 pounds per acre.

In the meantime, Frame pointed out that Virginia Tech’s current recommendation for nitrogen fertility in cotton is 50 pounds of nitrogen per bale of expected yield. He said the caveat in the recommendation is to account for cotton likely gaining 20 to 30 pounds of the nitrogen it needs from the soil.

“The optimum rates for nitrogen ranged from 102 to 160 pounds per acre depending on placement strategy. Frame recommends 20 to 30 percent of the nitrogen be applied at planting with 70 to 80 percent applied at side-dress. That’s either one or two applications depending on your system.

Virginia Tech’s current sulfur recommendation for cotton is 20 pounds to the acre. “We usually apply that with nitrogen. I would like to see 30 to 50 percent going out at planting. Cotton needs sulfur early in the season rather than later in the season, so we need to start splitting our sulfur applications,” Frame explained