If you bury cotton underwear in a field with no-till and a cover crop production system, you’ll find a pair of raggedy drawers when you dig them up in five weeks.
Bill Robertson, University of Arkansas cotton agronomist, makes that point when he talks about the value of a cover crop and reduced tillage system.
He reprised that demonstration at the recent Cotton Consultants’ Conference, the opening segment of the National Cotton Council’s annual Beltwide Cotton Conferences, held in New Orleans.
Robertson, along with University of Tennessee Institute of Agriculture weed researcher Larry Steckel and Mississippi State University research entomologist Don Cook, took a broad view of cover crop implementation in cotton, including the advantages but also the potential for increased insect pest control.
Robert Hankins Jones, RHJ Ag Services, Winnsboro, La., moderated the panel and explained that soil health has become an important factor as cotton farmers try to produce a more sustainable crop and grow it efficiently.
“We hear a lot about soil health,” Jones says, “but we don’t get to hear much about risk and rewards — mostly just the benefits.”
He says that was the reason to convene “a team of guys representing agronomy, weed science and entomology” to explore how cover crops are used in cotton. “The benefits, are many,” he adds, “but we see some risks.
“We often don’t know what cover crops to use and what the benefits are. Implementation may have been put before science.”
Robertson began the discussion. “What is healthy soil?” he asks. About half the volume consists of silt and clay and organic matter. “The other half is pore space, space for water and air. Compaction squeezes those pores out, so not much room is left for air and water.”
He adds that compacted soil can take in only so much water, even if irrigated.
Robertson also notes the stewardship advantage of cover crops and no-till production. “The cotton supply chain wants sustainable cotton,” he says. “Reducing the environmental footprint of cotton involves two main things — reducing tillage and using a cover crop.”
He says soil probes and monitors, plus a lot of other techniques, also contribute to improved stewardship.
“Often, we can sell cover crop use because of residue for weed suppression,” he adds. “For me, improved water infiltration and reduced compaction are the important benefits.”
Robertson says cover crops and no-till stimulate soil micro-organisms — bacteria, protozoa, nematodes, a ton of things that are good. “Not all nematodes are bad,” he says. Living things like fungi and nematodes break up soil.
Robertson displayed the underwear to prove his point. The pair of men’s briefs buried in a conventional cotton field were, although a tad worse for wear, still intact after five weeks. The briefs buried in the no-till cover crop field bore little resemblance to underwear.
“This is a visual representation of what goes on in the soil,” Robertson says.
He notes that increased water infiltration moves moisture deeper into the soil profile, stimulating root growth and increasing the plant’s ability to pick up nutrients.
Other practices measure moisture, what comes on and what leaves the field.
Steckel followed Robertson’s presentation, admitting that he had no competing visual representations, but noting that herbicide-resistant weeds prompt weed scientists to look for alternative means of control. “Cultivation is one option,” he says.
“We do not see a lot of new herbicides coming in, so cover crops may offer an opportunity in Tennessee.” Tennessee farmers have embraced no-till for years, so adding a cover crop may be the next logical step.
“We still have questions,” Steckel says. “What cover crop is best and what’s the best time to burn it down?”
He said early cover crop trials focused on protecting seedling cotton from sand blast injury. “It helps. But the cover crop and the plant populations used to prevent sandblast was not robust enough for good weed control.”
He says a PhD student took on cover crop research, looking at a blend of grasses and legumes. He also looked at time of termination.
Steckel says the research shows, “The closer to planting you terminate the cover crop, the better off you are with weed control.” Keeping weeds shaded out until the crop is established is an advantage.
Steckel says research on allelopathy — the chemical inhibition of one plant (or other organism) by another, due to the release into the environment of substances acting as germination or growth inhibitors — shows an advantage with cover crops. Residual control of Palmer amaranth, for instance, may extend by 14 days because of allelopathy. “It also reduces the number of pigweed plants that come up by 50 percent.”
He says cover crops may be part of weed resistance management and will help extend the life of dicamba. “That will be a win, win.”
No free lunch
Not so fast, says Cook. “Nothing in life is free. You’re talking about benefits. I’m talking about costs. We don’t have enough work yet on cover crops, especially terminating close to planting.”
He mentions the green bridge, a viable host crop that allows insect pests to survive after one crop is harvested until another emerges.
He says termination at least three weeks prior to planting is better, from an insect management perspective, than waiting until close to seeding.
“If you terminate close to planting,” Cook says, “be prepared for residual insect control.
“I’m afraid, and I hope I’m wrong, but when we get this on a bigger scale, we’re going to have anywhere from a few to a bunch of situations.”
He thinks producers may have to increase management and control costs for insect pests. He mentions slugs, wireworms, spotted mites, alfalfa hopper, thrips, and false chinch bugs, among other pests, that could be aided by green cover.
Cook says managing cover crop termination is a lot different from planting in old crop residue. “You want to be aware that you cannot manage this year-to-year like a burndown treatment. Expect additional management, which will depend on which cover and which field. We see a lot of possibilities.”
Cook says producers need to consider costs as well as benefits with cover crops. “I think we will see problems we’ve never seen in cotton. Can you imagine what a week’s worth of spider mites looks like? Normally, that means we’ve got a dead spot.”