Researchers Test Drip Irrigation Design And Returns
Writer: Tim W. McAlavy, (806) 746-6101,t-mcalavy@tamu.edu
Contact: James Bordovsky, (806) 889-3315,j-bordovsky@tamu.edu
HALFWAY – Crop producers on the Texas High Plains have long considered subsurface drip irrigation systems the “Cadillac” of irrigation technology. They maximize water use efficiency, boost crop yields in most cases and require less labor during operation due to automation.
But there is a drawback. Subsurface drip systems cost more to install. Turnkey installation of such a system, including filters and automated controls, ranges from $700 to $1,000 per acre.
Texas Agricultural Experiment Station scientists are currently testing and comparing subsurface drip irrigation systems to see how lower-cost designs affect water distribution, crop performance and total yields.
“The question is, can we reduce design standards for these irrigation systems – reducing their initial costs – and still get good yields,” said Jim Bordovsky, Experiment Station agricultural engineer based at Halfway. “We are in our fourth year of comparing cotton yields among three subsurface drip designs.”
Bordovsky is conducting this research with Dr. Dana Porter, Experiment Station and Texas Cooperative Extension irrigation specialist; Dr. Jeff Johnson, an Experiment Station and Texas Tech University economist, and Experiment Station research technician Joe Mustian.
The experimental drip system is made up of three groups of drip laterals, or tapes. Each group represents a different drip system design. The designs provide three levels of water distribution uniformity ranging from very good (representing a more expensive system) to poor (representing a lower cost system).
To achieve the three levels of water uniformity in the experiment, each design has a unique tape diameter and operating pressure with irrigation flow controlled independently of the other designs.
All tapes are installed on 60-inch centers and water two 30-inch rows. Emitters on each tape lateral are the same size and spaced 20 inches apart. All laterals are 1,320 feet long, roughly one-quarter mile. “The main differences in these designs are tape diameter and operating pressure,” Bordovsky said. “We grow one variety of cotton using planting and fertilizer rates that are common in the area.
“Within this experiment, we use two different irrigation regimes, each based on local evapotranspiration rates. In one regime we give the crop 100 percent of an estimated base irrigation rate. In the other regime, the crop receives 60 percent of the base irrigation rate.”
Irrigation in this study is applied as a supplement to rainfall from June through August. “2001, 2002 and 2003 were dry years, but we received record rainfall in 2004,” Bordovsky said. “Our rainfall in 2005 has been more typical, although an isolated hail event did affect yield. In order to compare crop yields among these three subsurface drip designs we take yield samples at five locations along each lateral line within each design.”
With four growing seasons behind them and another almost in the bag, the scientists have reached some preliminary conclusions.
“We have learned that environmental and physical factors can affect cotton yield uniformity as much as the irrigation system design,” Bordovsky said. “We’re talking about things like hail, blowing sand, insect or disease pressure, soil type and topography.
“We’ve also learned there isn’t much overall yield difference for an entire field among the three different subsurface drip designs at 60 percent of base irrigation. Our total average yields have fluctuated in a very narrow range, from 1,299 pounds per acre to 1,304 pounds per acre.
But the scientists have noted a difference in water uniformity across the field among the three systems.
“Reducing the design standards will lead to less-than-perfect water distribution and greater yield variation along each row,” Bordovsky said. “The yield we get down the furrow is correlated to how the system distributes water. Poor distribution of pre-plant irrigation could really have an adverse effect on cotton germination in dry years.
“Even so, these experiments indicate that we could reduce the design standards and, therefore, the initial cost of subsurface drip systems without affecting overall cotton yield.”
The scientists also plan to conduct an economic analysis to compare operating costs with total yields produced in each of the three designs.
“We hope to have the economic analysis done sometime in 2006,” Bordovsky said.
The Texas State Support Committee of Cotton Incorporated and the United States Department of Agriculture’s Agricultural Research Service Ogallala Research Initiative provided financial support for this research.
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