Researchers: Timing critical when watering High Plains cotton

LUBBOCK – In semiarid farming regions where every drop of water counts, Texas AgriLife Research scientists say timing the application of available water is becoming more critical when it comes to irrigating cotton.
Jim
Jim Bordovsky, research scientist and agricultural engineer with AgriLife Research at Halfway, is collaborating on a project with Drs. Dana Porter and Jeff Johnson, Lubbock-based Texas AgriLife Extension Service agricultural engineering specialist and AgriLife Research economist, respectively.

They recently completed the second year of a study to optimize water-use efficiency, lint yield and fiber quality of cotton under limited water conditions by evaluating a combination of irrigation amounts during different growth periods using Low Energy Precision Application or LEPA irrigation.

Bordovsky said the growth periods used in the study are generally described as: vegetative – from planting until very early bloom; reproductive – early bloom to just past peak bloom; and maturation – bloom to initial boll maturity. Their overall objective was to improve water efficiency in the semiarid Texas High Plains region by learning when a cotton crop responds best to combinations of limited and adequate water.

“Our irrigation water comes from the declining Ogallala Aquifer, where its availability for a given field can change dramatically within a single growing season,” Bordovsky said. “Shortages also occur when producers must divert water from cotton and give it to another crop, because that crop has reached a critical growth stage or simply because it’s worth more. Abrupt changes could also occur if irrigation wells are lost or annual irrigation volumes imposed by regulatory mandates are reached before the end of the growing season.”

Bordovsky said wise planning of irrigation based on a farm’s underground water resources, available water allowances and the region’s erratic rainfall will go a long way toward High Plains producers being productive in coming years.

“In situations where available water can’t meet the needs of the plant throughout the growing season, the irrigation-research community has recommended and producers have generally followed the practice of ‘banking water’ or attempting to partially fill the soil profile with preplant and/or early-season irrigations in April through June,” Bordovsky said.

“While a full profile is very desirable and preplant irrigation is absolutely necessary in some years, our work indicates that under potential water constraints, the strategy of filling the profile by irrigation may need to change or at least be tempered for irrigated cotton.”

That’s because with typically high wind speeds, high air temperatures and low humidity in the spring, it’s extremely difficult to retain early applied water in the soil until the time when cotton plants really need it in July and August, he explained.

“In addition, early season water applications exceeding crop water demand can be lost through evaporation or excessive plant growth, which translates to non-productive water use and the potential of running out of restricted water units before the end of the growing season.”

Bordovsky and his team gathered data from two very different years with record-breaking extremes, high rainfall in 2010 and the drought of 2011, and saw similar results when irrigation timing was considered.

“During the record-setting drought of 2011, research results indicated that trying to store water in the soil profile in excess of the cotton plant’s evapotranspiration rate during the month of June was ineffective. That was the second year of the study, but the 2010 data collected during a wet year indicated the same thing.”

So when is the best time to water?

Based on results to date, Bordovsky said producers should ensure they have irrigation available in the reproductive and early maturation periods of cotton development. In this study, water applications resulted in more than 100 pounds of cotton fiber per acre-inch of irrigation during these latter periods compared to less than 20 pounds per acre-inch from water applied above the crop water demand during the vegetative or “water banking” period.

“Additional field tests should provide the foundation for in-season irrigation recommendations for producers with specific irrigation volumes and irrigation capacities,” Bordovsky said. “We hope that the eventual findings will help High Plains cotton producers optimize their total water use when faced with limited water volumes.”

Bordovsky said this research is supported in part by the Texas State Support Committee of Cotton Incorporated and the U.S. Department of Agriculture-Agricultural Research Service Ogallala Aquifer Program, a consortium among the U.S. Department of Agricultural Research Service, Kansas State University, AgriLife Research, AgriLife Extension, Texas Tech University and West Texas A&M University.

For more information contact Bordovsky at 806-746-6101, j-bordovsky@tamu.edu .

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