Timing is critical when watering High Plains’ cotton
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.
• Timing is the key when watering cotton on High Plains.
• Researchers look at irrigation in different growth periods.
• With limited water, growers may need to target watering.
Jim Bordovsky, research scientist and ag engineer with AgriLife Research at Halfway, is collaborating on a project with Dana Porter, Texas AgriLife Extension Service agricultural engineering specialist, and Jeff Johnson, AgriLife Research economist, both based in Lubbock.
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 irrigation amounts during different growth periods using Low Energy Precision Application, or LEPA, irrigation.
Bordovsky says 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
• maturation — bloom to initial bloom maturity
Their overall objective is to improve water efficiency in the semiarid Texas High Plains 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 says. “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 says 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 says. “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 notes.
“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,” he says.
Bordovsky and his team gathered data from two very different years with record-breaking extremes, high rainfall in 2010 and the historic 2011 drought, with 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’s 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 says producers should ensure they have irrigation available in 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 says. “We hope that the eventual findings will help High Plains cotton producers optimize their total water use when faced with limited water resources.”
This research is supported in part by the Texas State Support Committee of Cotton Inc. and the USDA Agriculture Research Service’s Ogallala Aquifer Program. For more, contact Bordovsky at 806-746-6101 or email firstname.lastname@example.org.
Byrns is with Texas A&M Agriculture Communications, San Angelo.
This article published in the June, 2012 edition of THE FARMER-STOCKMAN.