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Waterlogged soils can severely damage cotton
Texas
Heavy rain and unseasonably cool temperatures have presented a unique situation for cotton farmers in the Central Texas and Gulf Coast regions. Many crops are now standing in water during a critical stage during the growing season.
"Waterlogging of a field for several days reduces the crop growth rate and can potentially reduce yield," said Dr. Robert Lemon, Texas Cooperative Extension state cotton specialist. "Generally speaking, waterlogged conditions reduce the crop growth rate by replacing the air in the soil with water, depriving the root system of oxygen."
Since oxygen diffuses more slowly through water than air, the roots become deprived of oxygen and are unable to maintain normal respiration, Lemon said.
"Respiration is a necessary process that the plant uses to provide energy and building blocks for growth," he said. "As a general rule, respiration rates are greatest in the meristematic tissues of the growing points, such as the terminal and the root tips."
Waterlogged soils are anaerobic (without oxygen). Some of the effects are: chlorotic, yellow plants; reduced growth rates; reduced photosynthesis and respiration; reduced nutrient uptake; and altered plant hormone levels.
"If we couple the wet soils with the moderate temperatures and reduced sunlight conditions over the past few weeks, it all adds up to a crop that has gotten off to a very slow start," he said. "And that may be an understatement."
Waterlogged conditions inhibit plant hormones that contribute to growth. Gibberellic acid and cytokinins are hormones that contribute to growth and leaf expansion. Producers should be careful about applications of mepiaquat chloride (Pix, Pentia -mepiquat pentaborate, etc.) "during this stressful period," Lemon said.
"Since most fields are already under stress and are experiencing slow growth due to the reduced production of these phytohormones, we need to be careful about these applications," he said.
"The primary action of these products is to reduce gibberellic acid production in the plant, which reduces internode and leaf growth. Because mepiquat chloride suppresses plant growth, it can have harmful effects on stressed plants by further limiting growth."
Lemon said dry, warm conditions are needed to stimulate growth. Applications of these plant growth regulators will suppress growth and slow the recovery process.
"Once the crop has returned to a healthy condition, monitor the fields and apply plant growth regulators as dictated by plant growth," he said.
Health and size of the root system. "Generally speaking, the cotton root system grows rapidly during early season," Lemon said.
During the vegetative stage, root development may proceed at a rate of one-half to two inches per day, and after 40 to 50 days the root system may be three feet deep, he said.
"Unfortunately, the wet conditions have restricted root development, and this could be a factor during flowering and boll fill," Lemon said. "Whenever it dries enough to cultivate, be careful not to set the sweeps too deep or too close to the plant. The last thing we need to do is prune the root system."
Will foliar feeding the crop provide benefits? "Most research indicates that foliar feeding with nutrients, or applying plant growth products will not provide much benefit to young, stressed cotton," Lemon said.
"The crop is experiencing multiple problems and although its appearance may be slightly improved, a yield response is unlikely. The plant is struggling to grow, photosynthesis is impaired, and nutrient uptake from the soil is reduced. As a result, the utilization of foliar nutrients will be limited."
The cotton plant needs to accumulate a certain amount of heat units throughout the season. The heat unit (growing degree days) is a measure of the amount of useful heat energy the plant accumulates each day throughout the season.
"The cotton plant must accumulate a certain number of heat units for it to reach certain developmental stages," Lemon said. "The optimum temperature for cotton growth is about 90 degrees. At lower temperatures, the developmental rate will be slower. This season we've experienced moderate temperatures, wet conditions, and an overabundance of cloudy days."
All these factors have reduced the growth rate of the cotton crop, he said, and node development is a reliable indicator of crop progress.
"The bottom line is that we need warm temperatures and sunshine to 'kick-start' the crop," Lemon said. "Nothing we can do to this crop can replace good growing conditions."
Date: 6/24/04
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