Cotton crop can hold off on that drink
The idea that cotton plants are large water consumers has largely been relegated to a myth, but irrigated cotton still displays greater yield than dryland cotton — even with deficit irrigation, when it is done on time.
Jim Bordovsky, an agricultural engineer and senior research scientist at the Texas AgriLife Research and Extension Center at Halfway, is trying to pinpoint that time period. Applying a variety of irrigation rates during three different growth periods, he is finding that irrigation at the beginning of the season may not be as efficient as later applications.
“We are getting supplemental irrigation water from the Ogallala Aquifer, which is not being recharged at the rate it is being used, so pumping capacity declines from one year to the next as well as over the growing season,” he says. “Because the ability to deliver water is becoming more difficult, the question becomes: When do we apply available units of water during the growing season to get the most value out of these units of water?”
• Texas research shows later watering can help cotton yields.
• Timing of deficit irrigation is critical to crop vigor.
• Research holds key to production in an ongoing drought.
Using university land, the research project is supported by the USDA Agricultural Research Service Ogallala Initiative and the Texas State Support Committee of Cotton Inc. The research fields were divided into plots receiving a different individual irrigation treatment throughout the season, based on water-holding capacities determined by pre-planting soil samples.
The samples were recorded into a computer, which was used to create a detailed irrigation map of the plots. Those maps were uploaded into a pivot irrigation system modified to vary the applications according to the treatments.
The treatments fell between two extremes. Plots on one end received no supplemental irrigation during the growing season, while plots in the other extreme were treated with a quarter-inch per day in three growth periods, the highest capacity of all treatments. There were 25 other treatments with varying combinations of treatments and growth periods.
The first growth period lasted from planting through first bloom, or up to 950 heat units. The second began at the end of the first period up to 1,300 to 1,400 heat units, when the cotton is blooming heavily. The third application was boll maturation.
After two seasons, Bordovsky found later applications were much more critical to yield than earlier applications. “The water applied during the first part of the growing season resulted in lower irrigation productivity than water [applied] at the middle and end of the growing season,” he says. “Water applied at the end of the season resulted in the highest water productivity and yield.”
The 2010 and 2011 growing seasons were vastly different due to the higher-than-average precipitation in 2010 and a severe drought in 2011.
“We had two weather extremes, and anyone looking at the results should understand the limitations [of the results],” he notes.
Even so, the results still seem to indicate irrigation water applied to cotton at the end of the growing season is the most important.
More research to come
Bordovsky plans to continue the research through at least the next few seasons to provide growers with the best treatment sequence. It is especially timely in the face of a severe drought in Oklahoma and Texas, as well as the Southeast droughts, which are likely to continue at least through the next season.
“If growers have a way to save water and money through pinpointing the plant’s ability to optimize water usage, they could protect groundwater supplies and salvage at least part the crop in severe droughts.
“Either water policies will set irrigation volumes, or the ability to pump water from our wells will be limiting, so trying to find the most effective time to apply limited irrigation is important,” says Bordovsky.
Brazil writes from Carnegie, Okla.
This article published in the February, 2012 edition of IRRIGATION EXTRA.
All rights reserved. Copyright Farm Progress Cos. 2012.