In the late 1970s, with the U.S. farm economy reeling from two major oil crises, an Auburn University agricultural engineer — W.T. Dumas — began research on developing a cotton production system that would allow growers to plant into crimson clover, thereby providing a perpetual source of nitrogen. This experiment, conducted in the small east Alabama town of Marvyn, led to further efforts at designing conservation-tillage systems for use in cotton production.
In recent years, thousands of Southeastern cotton acres have been converted to conservation-tillage. In Georgia alone, 250,000 to 300,000 of the state's 1.5 million-acre cotton crop are expected to be planted in some type of conservation-tillage this year, mostly in the form of strip-tillage.
During this winter's Georgia Cotton Production Workshop, members of the University of Georgia's Extension Cotton Team, led by Extension Cotton Specialist Steve M. Brown, shared their thoughts on the use of conservation-tillage in cotton production. The following is a summary of that discussion.
Growers who choose to make the switch from conventional to conservation-tillage should begin planning well in advance, says Glen Harris, Extension soil scientist. “If you can get your soil into good shape prior to beginning a strip-till system, it'll make things easier when it comes to liming and fertilizing,” he says.
Harris advises growers to correct any nutrient or pH problems throughout the plow layer before planting in a conservation-tillage system.
“In most cases, you'll be converting from a conventional, deep plowing system. If you're converting from a chisel plowing system, it'll be more difficult, but you can use that last opportunity to get some pH and phosphorus and potassium incorporated into the soil,” says Harris.
Fertility and pH can be maintained in a strip-till system with surface applications if a grower starts off right, he adds. “You cannot correct problems later if you don't start off right. If you have a pH problem down to eight inches, throwing lime on top of the soil will not solve it.
“One of the hardest things for a grower to believe is that he can do a good job with pH by making surface applications. After you've been in a conservation-tillage system for about three years, we recommend taking a more shallow soil sample, at about two to three inches. A pH problem will develop on the top and work its way down.
“It's best if you can catch a problem with a shallow soil sample and correct it with a surface application of lime before it gets too deep. I've seen situations where growers have gone for five or six years, and the pH problem has gone too deep. The only option for these growers is to plow or chisel in some lime. Once the problem gets too deep, it's difficult to correct with surface applications.”
Poultry litter, notes Harris, is an option for fertilizing in strip-till situations. “If you can't put poultry litter on before you do the strip-till operation, you at least can incorporate some into the strip. We think we might lose a little nitrogen from poultry litter in a conservation-tillage system.
“We typically have 60-percent available nitrogen from poultry litter in a conventional system. It probably goes down to about 50 percent in strip-till systems. You'll lose about 10 percent available nitrogen. Three years of research has shown that poultry litter works fine on cotton in a strip-till system. Those same studies show that poultry litter decreases the yield of peanuts, but Alabama research shows favorable results from using litter on peanuts.”
Growers have several possibilities when selecting a cover crop for their strip-till cotton system, says Harris. Initial research focused on planting a legume crop in a conservation-tillage system, but this proved to be challenge, he adds.
“Most growers have gone to small grain covers or winter weed and old crop residue. About 95 percent of the cover crops in Georgia will be rye or wheat. But there's a renewed interest in legumes because of rising fuel and nitrogen prices.”
Harris advises growers not to fertilize their cover crops unless they want to work with a large amount of residue. Rye, especially, can become difficult to kill if it grows too large.
“How much residue should a grower make? I'd say as much as you can handle. But don't jump into strip-till for the first time with a lot of residue. Strip-till is a new game, and until you get used to it, you might want to consider starting with winter weeds and graduating to wheat, and then to rye with fertilizer.
If a grower plants cotton following a small grain cover, he should increase the nitrogen by about 25 percent, says Harris. “And I'd like to see that nitrogen applied preplant to take care of the residue and make it more mellow. If a grower plants cotton following a legume, he probably can decrease the nitrogen rate.”
The most critical pieces of machinery for strip-tillage cotton production are a strip-till unit and a burndown sprayer, says Michael Bader, Extension engineer. Foam markers also can be helpful to prevent leaving strips in the field, he adds.
“If we stay with a conservation-tillage system year after year, and maintain the integrity of row patterns, we probably can eliminate subsoiling in our heavier soils,” says Bader. “In our sandier soils, we probably can eliminate subsoiling if we control our traffic. But it's difficult to control boll buggy and dual picker traffic, so it's probably best to continue subsoiling in sandier soils.”
More seedling disease
Southeastern producers probably will find a higher incidence of seedling disease in conservation-tillage cotton, says Bob Kemerait, Extension plant pathologist.
“Increased organic matter gives pathogens something to feed upon,” he explains. “The cooler soil temperatures and higher soil moisture associated with conservation-tillage also encourages soil-borne seedling diseases.”
But, he adds, there also are benefits in conservation-tillage that should help to reduce the incidence of seedling disease. “Organic material in the ground will increase the microbial flora and fauna associated with the soil, and this will give us benefits. One of the best things we can do to reduce seedling disease is to encourage rapid, vigorous growth of the cotton plant. If conditions are warm enough, the increased soil moisture in conservation-tillage will help with rapid germination of the seed,” says Kemerait.
Before using an in-furrow fungicide in conservation-tillage, Kemerait advises growers to consider several factors at planting time. “Consider the history of the field, the soil and air temperatures at the time of planting and the projected weather forecast. Often times, it won't be economically beneficial to use an in-furrow fungicide.”
Strip-till insect pressure
Seedling insects, such as early season thrips, often are associated with conservation-tillage, says Phillip Roberts, Extension entomologist. “But a lot of data has shown that we have fewer thrips in strip-tillage versus conservation-tillage. But by no means would that allow us to stop using a preventative insecticide at planting,” he says.
Cutworms are a potential problem in cotton strip-tillage systems, notes Roberts. “The risk of having problems with cutworms definitely increases in strip-tillage. In conservation-tillage, cutworms can become established on winter weeds or covers, particularly legume covers.
“We need to burn down the cover crop in a timely fashion — at least three weeks prior to planting. Cutworms may linger until cotton emerges from the ground. And cutworms are more of a problem in legumes than in wheat or rye,” he says.
If a grower is in a high-risk situation where he suspects a cutworm problem, it might prove effective to band a pyrethroid behind the planter, says Roberts.
Many conservation-tillage growers experienced problems with false chinchbugs this past year, says Roberts.
“False chinchbugs were established on cover crops, and many growers were forced to replant because of this problem. We can avoid this problem by burning down on a timely basis and removing that host plant. We can see this same problem in Roundup Ready cotton where we have a lot of weeds in a field. Insects can become established on the weeds. Then, when we remove the weeds, the insects move to the cotton.”
It can be said that beneficial insect activity is greater in conservation-tillage because there are more fire ants, says Roberts. “Fire ants are good predators, helping us with corn earworms and tobacco budworms. But we see aphids build more rapidly wherever we have fire ants. Fire ants protect aphids from other predators.”
Weed control strategies
Cutleaf evening primrose is a major problem in conservation-tillage cotton production because paraquat and glyphosate are not very effective in controlling the weed, says Stanley Culpepper, Extension weed scientist. Herbicides are available that will effectively control cutleaf evening primrose, but these materials have many restrictions, he says.
Wild radish and Florida pusley also are becoming major problems in strip-tillage systems, adds Culpepper. “Most growers who till their fields put out a DNA herbicide to control Florida pusley. If you're strip-tilling, and Florida pusley already has come up, there's not a consistent, effective, postemergence herbicide available to control the weed,” he says.
It's critical, says Culpepper, that a grower who has problems with cutleaf evening primrose, wild radish and Florida pusley, use 2,4-D in strip-till situations.
“We need to put out this application of 2,4-D 45 days prior to planting, which means late February or early March for most of our growers. You don't have to apply 2,4-D with Roundup or paraquat to take care of those weed species. If you use 2,4-D alone, it'll allow you more flexibility at planting.”
Culpepper says he would prefer using a small grain as a cover crop rather than winter weeds. “It's easier to kill a small grain than it is to kill winter weeds.”