Cotton farmers don’t have enough information about how specific varieties perform under various levels of water availability—either from rainfall or irrigation—according to a private researcher and consultant.

“We ought to know how much water it will take to make one bale of cotton with a specific variety and how much and when to apply it and how much moisture we have in the profile. We don’t always know that,” says Bob Glodt, president of Agri-Search in Plainview, Texas.

He’s testing varieties for Deltapine on his 140-acre research farm to identify how those varieties respond to certain water regimes—from rainfall only to applying 90 percent of evapotranspiration (ET) replacement. He also works with other companies on various research products and counts Bayer CropScience, Americot, FMC, BASF, and DuPont among his clients. He also consults with eight farmers.

“I am reluctant to appear to be a spokesman for any company,” Glodt said, but he’s convinced the irrigation/variety study is needed across cotton country.

“This research involves responsible, sound water management, and I am glad to be a part of it.” He works with Doug Jost from Monsanto who says the goal from his perspective is to identify varieties that perform well under a wide range of climate conditions, from limited rainfall to meeting near full moisture demand.

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“I think we are gaining insight into some long-held but wrong views about cotton water needs,” Glodt said. “This has been some of the most interesting work of my career.”

He bought the research farm in 2006. “Monsanto asked then if I would be willing to do water efficiency trials. I’ve been involved in the study since then.”

Each year Glodt sets up tests for eight to 12 varieties, replicated four times and under four different irrigation treatments—no irrigation, 30 percent, 60 percent and 90 percent ET replacement. “That covers just about every irrigation regime possible in this area.”

Trials included 194 plots and 12 varieties this year.

Irrigation regimes

He modified a center pivot irrigation system to apply a certain amount of water per application on 16 rows, a different amount on the next 16 rows and a different amount on the other 16 rows. He plants all plots at the same time, manages them the same and waters them at the same time “to see how varieties will respond. At the end of the year, we know. The data is applicable to cotton over a wide range.”

Yields are the benchmarks. “We want to determine how much 1 inch of water or 2 inches of water buys in yield,” Glodt says. Some varieties, he’s found, do not take advantage of increased irrigation. “That was an eye-opener. When we irrigate, that comes out of our back pocket as opposed to free irrigation, rainfall. Not all varieties are created equal in response to increased water. And not all varieties respond the same to lower water regimes.”

The point is, Glodt said, farmers need to know which varieties will take advantage of extra water and which will perform adequately, or at least better, when rainfall or irrigation capacity is limited. “This is powerful information. Over the years we have developed a lot of variety data, and I wonder why we haven’t done this kind of research before.”

Jost has some ideas. When cotton farmers began to get comfortable with new technology—herbicide tolerant and insect resistant varieties—weed competition and insect damage became less limiting factors. Also, water availability began to become a more crucial issue, made even more so by several years of drought.

Water conservation

Glodt is aware of a growing need in the Texas High Plains to conserve water. He’s an agronomic advisor to the Texas Alliance for Water Conservation , an organization that seeks ways to improve on-farm (and other) water management. “TAWC tries to educate farmers on new irrigation technology and irrigation management approaches while conserving irrigation resources,” he says.

He applies a lot of what he learns from research trials to his farm clients. “Every company should be doing this kind of work,” he says. “If a farmer plants a 90 percent ET variety in a 30 percent ET regime, he may not be happy with the yields he achieves at the end of the year.”

Trials have helped establish a standard. “Before these tests I couldn’t estimate yield potential for 30 percent or 60 percent ET replacement. Now, I’m better able to do that.”

He said test results will show farmers which varieties are more likely to perform well on dryland acres and which will respond to increased irrigation water. He wants to know how many inches of water he needs to apply to produce two and three-fourths to three bales of cotton. “At 60 percent ET replacement, two and-a-half to three bales should be possible. Some years, with 90 percent ET replacement (including rainfall) we should hit four bales.”

One of four years might see 90 percent ET replacement and four-bale potential, he added. “In the other three years we might get by with 60 percent ET or a little better but with possible quality loss.”

He does not advocate irrigating at 90 percent ET. “Save the water and irrigate based on potential ET and look at the cotton water demand curve to determine application timing.”

Use available tools

He says most farmers do not have the irrigation resources to over-irrigate the crops they grow; however, better yields can be achieved when irrigation is applied at a specific percentage of potential evapotranspiration (PET). If a grower has the capacity to irrigate at 30 percent ET replacement, this amount of water should be applied to coincide with crop water demand. Then start connecting the amount of water applied to potential yield of the variety.”

Jost says the trials always include several check varieties as measuring sticks for newer lines. “We’ve used 1044 as a standard check because it does well with limited water. We have been able to beat 1044 consistently with some new varieties, so we’re making progress.”

“I was skeptical when we first started,” Glodt says. He’s now convinced that cotton farmers need to look at several factors to determine when and how much to irrigate. Variety selection will be one of those. He also advises growers to use TAWC PET data (www.tawcsolutions.org) and Texas Tech Mesonet data to determine moisture demand. “That is critical. Even farmers who have water have to manage it right. The big dividend comes when we learn a little about water management.”