Preventing, or at least delaying, development of herbicide resistant weeds may be one of the most important advantages of a systematic rotation in cotton production.
Other advantages, according to Robert Lemon, former Texas Extension cotton specialist, include accumulation of crop residue, improved soil moisture, better fertility management, improved pest management, opportunity to diversify market opportunities and the “rotation effect.”
Lemon, who recently left Extension and is now consulting with AgriThority, discussed the importance of rotation for Texas cotton producers at the Beltwide Cotton Conferences in San Antonio.
“Rotation is one of our most important practices,” Lemon said. “Benefits are well documented all the way back to the Roman Empire.”
He explained the “rotation effect,” as an intangible, difficult to understand benefit. “But we know it’s there.”
More tangible, he said, are advantages with weed control and resistance management. “We’ve been fortunate so far in Texas with resistance issues. We’ve seen some water hemp resistance in South Texas, but rotation with grain sorghum helps. We do a pretty good job of managing resistance with a crop like grain sorghum because we get a triazine herbicide into the mix.”
He said as Texas moves into energy bio-fuels production, crops such as sweet sorghum will offer new rotation options and better opportunities to manage weed resistance.
“In the Texas High Plains, we have Palmer pigweed, but growers do a good job using yellow herbicides. Grain sorghum will assist in preventing herbicide (glyphosate) resistant pigweeds.
“Prevention is the key. If you don’t have the problem, you don’t want to get it.”
Lemon said Texas cotton farmers “have embraced rotation,” especially as the value of grain and seed crops have improved.
He said rotation crops may help farmers save on fertility. “We’ve done nitrogen management studies for several years across the state in producer fields and have found carryover nitrogen with depth. In cotton behind cotton we find less nitrogen than we do behind other crops.”
He said deep nitrogen use studies show benefits from residual nitrogen. Studies show that crops use efficiency of nitrogen applied at a six-inch depth is 75 percent. At 18 inches, efficiency is almost 70 percent. “Efficiency begins to drop off at 30 inches to 42 inches,” Lemon said. “But nitrogen down to 2 feet is beneficial. Findings are not surprising.”
He said profiles with significant amounts of nitrogen show up in 61 percent of test sites. He says 24 percent of the study sites show a response to deep nitrogen. “There is value in deep nitrogen.” Rotation behind grain sorghum corn or soybeans helps maintain that residual, he said.
He also encouraged producers to know how much residual nitrogen they have. “Soil test annually and test to depth,” he said. “You can save money.”
Rotation options vary across Texas. “In the southern and eastern parts of the state, corn and grain sorghum may be the most widely used rotation crops. But producers are looking at sesame, sunflowers, canola and high bio-mass sorghum.
“In west Texas, peanuts offer a good rotation option. Most of our peanuts are grown on the High Plains,” Lemon said.
He said wheat has become a more popular rotation option for cotton, “especially with irrigation. And grain sorghum has always been a good rotation crop with cotton in west Texas.”
Crop rotation also helps manage weed, insect and disease pests by “breaking up the complex.”
Jimmy Dodson, a cotton and grain producer from Nueces County, Texas, moderated the rotation panel and said the last few years brought “unusual circumstances and caused us to look at cropping practices in a new light.”
One word from a producer’s point of view characterizes the last 12 months, he said. “Volatility was apparent in commodity markets, credit markets and weather. We saw different rotation crops like sunflowers, canola, sesame, specialty corn and wheat. We had a significant amount of wheat in south Texas for the first time. And we had some surprises — some pleasant and some not. Each crop comes with a different management profile.”
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