Cover crops have become an important tool for maintaining soil health and controlling winter weeds for Louisiana farmers. AgCenter researchers are exploring ways to obtain the best results from using cover crops.

Brenda Tubaña, Jack E. and Henrietta Jones Endowed Professor in the School of Plant, Environmental and Soil Sciences, is evaluating how winter cover crops can benefit soil quality and nutrient cycling. Her regimen with soybeans includes planting a cover crop after harvest, then following with a herbicide burndown four to six weeks before planting and finally planting a cover crop after harvest.

“The cover crop returns nutrients to the soil, and more biomass returns more nutrients to the soil when the cover crop decomposes,” she said.

In addition, the cover crop acts as mulch to hold down weeds, preserve soil moisture and prevent wind or water erosion.

To increase the effects of more biomass, Tubaña has added an application of 15 pounds of potash and 15 pounds of phosphate as a starter fertilizer when planting the cover crop. She has varied planting dates from immediately following the soybean harvest to as long as two months following harvest.

“Planting date has more influence on biomass,” she said. “September versus November planting is like night and day,” with a much better stand following earlier planting.

Tubaña uses a combination of crimson clover, hairy vetch and tillage radish as a cover crop. “We typically have grasses, legumes and crucifers in the cover crop mix,” she said.

The clover and vetch add nitrogen to the soil to encourage decomposition of the cover crop following burndown and tillage radish increases sulfur levels in the soil. Tillage radish poses a problem for no-till fields because the fibrous tops poke out of the soil, so the field has to be mowed to provide a clean seedbed for planting.

At the Northeast Research Station in St. Joseph, Josh Copes, LSU AgCenter agronomist and weed scientist, is evaluating the compatibility of winter cover crops with different fall residual herbicide treatments to control annual winter weeds. The goal is to identify cover crops that tolerate residual herbicides and provide competition to winter weeds.

“We want to select the cover crop and herbicide combination to match the main crop and manage winter weeds,” Copes said.

The program includes planting a cover crop of cereal rye, tillage radish, crimson clover or Austrian winter pea in combination with the herbicides Zidua, Valor, Bounty and Leadoff. The herbicide prevents growth of weeds from seeds returned to the soil within 30 days of harvest and controls plants that escape harvest. Cereal rye was the most effective as a competitor to winter weeds and was easily terminated four to six weeks prior to planting. Zidua was the least harmful residual herbicide on the cover crop and was the most effective for controlling winter weeds, particularly Italian ryegrass.

Copes applied the herbicides in October and terminated the cover crop in late January. The residual herbicides were selected to be friendly to the anticipated main crop, and the burndown herbicide was applied to allow a 30-day plant-back window prior to planting the main crop. Richard Bogren