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Irrigation Efficiency

System upgrade can help reduce water losses

        Irrigation application efficiency is defined as the amount of water stored in the soil available for crop use following an irrigation application, compared to the amount of water pumped, expressed as a percentage.

    Water losses occur during irrigation applications as a result of evaporation from the surface of water flowing down an open ditch or set of furrows; from water sprayed into the air above the soil surface by a sprinkler system; from plants that are wet during the irrigation application; from the wet soil surface area following irrigation; from irrigation tail water; and from deep percolation when more water is applied that the soil plant root zone can hold.

    The efficiency of all types of irrigation application systems used in the 15-county High Plains Underground Water Conservation District No. 1 service area have been evaluated under all weather conditions by Water District and USDA-Natural Resources Conservation Service (USDA-NRCS) personnel. Climatic conditions at the time a system is being evaluated affects the results of the evaluation by serval percentage points when compared to an evaluation on the same system under different climatic conditions. Temperature, wind velocity, and humidity are major factors in water loss. Other contributing factors are nozzle pressure, nozzle type, and wear as it affects water drop size and distribution patterns.

    Maximum irrigation application efficiencies can be achieved by utilizing a buried drip line irrigation system where no water migrates up to wet the soil surface. This system is usually considered to be 98 to 100 percent efficient.

    The second most efficient irrigation system available is the Low Energy Precision Application (LEPA) center pivot system. This type of system delivers water through drag hoses or socks that wet a narrow band of soil in the furrow in every other row of the crop. Furrow dikes hold water applied at a rate grater than the soil infiltration rate until it soaks into the soil. This type of system is 95 to 98 percent efficient.

    The following efficiency values are approximates based on the average results of hundreds of on-farm evaluations performed by Water District and USDA-NRCS personnel.

    LEPA center pivot systems, which have been modified by removing the drag hoses and/or drag socks in order to spray water near the land surface in an effort to wet the total soil surface area for germination of seeds of crops planted in dry soil or to provide a moist soil for planting seeds, have an application efficiency of about 90 percent.

    Partial drop center pivot systems, which deliver the water with spray nozzles approximately four feet above the soil surface, have water losses of about 20 percent. The water losses increase when the crop is two to three feet tall and the crop canopy is wet during irrigation. When the crop grows above the height of the discharge nozzles and shades the ground, the water losses decrease a few percentage point.

    Center pivot systems with drops 5 to 6 feet above the land surface generally have water losses of about 30 to 35 percent, depending on crop size, water drop size, and climatic conditions.

    Side row sprinkler systems are about 50 percent efficient, as are hand-moved systems.

    Water losses of 50 percent or more have been measured where old mortar joint cement pipe is used to transport water from the well to the field. Most of this water loss is caused by leaks at the joints, allowing water to seep below the pipeline. Although much of the water will eventually return to the aquifer, the fuel, labor, and replacement cost for equipment to pump the re-circulated water, plus the loss of yield potential, is likely to equal the cost to replace the pipe in a short time.

    Furrow irrigation where gated pipe is used in conjunction with high quality underground pipe or surface pipe and with no irrigation tail water loss is about 60 percent efficient. Furrow irrigation using a surge valve with gated pipe in conjunction with high quality underground or surface pipe and no irrigation tail water loss is about 80 percent efficient.

    In the High Plains Water District, ground water is pumped from the Ogallala Aquifer to make up the difference between the crop water demand and precipitation captured and stored in the soil prior to and during the crop growing season.

        We are thankful that 70 percent or more of the irrigated farms in the Water District have irrigation systems with application efficiencies of at least 80 percent. We salute producers who have prepared for this drought by upgrading their irrigation systems. Without this massive effort and expenditure, irrigated crop yields would have been much less.

    Research results from the Texas A & M University Research and Extension Centers at Amarillo and Lubbock indicate average crop production per acre-inch of timely irrigation water on a three-to-five year running average is 700 pounds of corn; 500 pounds of grain sorghum; 100 pounds of cotton lint; or five bushels of wheat.

    At a minimum, the loss of one acre-inch of water causes a decrease in potential yield by 50 pounds of cotton lint per acre; 250 pounds of grain sorghum per acre; five bushels of wheat per acre; or 350 pounds of corn per acre.

    Also, it is important to remember that three to four dollars of energy costs are paid for each acre-inch of water pumped and lost to evaporation. Pumping water when no benefit is received by the crop costs the producer money and wastes the landowner's ground water resources.

NOTE:  This information was provided by "The CrossSection" (a monthly publication of The High Plains Underground Water Conservation District No. 1, located at 2930 Avenue Q, Lubbock, Texas  79405-1499.   Telephone   (806)762-0181 or you can visit their web site at www.hpwd.com .