Resource Magazine July/August 2012 : Page 5

are building infrared thermometers that can measure canopy temperatures and indicate the level of water stress. Canopy temperature measurements can be used as a trigger to tell the grower, or the irrigation system directly, when irrigation should be started. Recognizing the importance of sustaining the High Plains Aquifer as long as possible, the USDA-ARS began the Ogallala Initiative in 2003 with the mission to sustain rural economies through water management technologies. Through this program, the USDA-ARS funds water management proj-ects in Texas and Kansas in a consortium with Kansas State University (KSU), Texas A&M University, Texas Tech University, and West Texas A&M University. Western Kansas ASABE member Freddie Lamm, an agricultural engi-neer at the KSU Colby Research Station and the ARS Central Great Plains Research Station, has been researching the use of subsurface drip irrigation in the High Plains for 23 years. He has shown that the systems can last that long if they are well maintained, and that they are a viable water-saving option for several of the crops grown in the region. With sub-surface drip irrigation, the water is precisely placed in the soil root zone and uniformly distributed across the field to help maximize its productivity. Surface evaporation losses are minimized since the crop and soil surface are not wetted. Although the initial cost of drip systems is high, the resulting water conservation, high yields, and long life can combine to make drip systems a good economic choice. One of the main irrigation limitations in many areas of the central High Plains is that the High Plains Aquifer is not very thick, and growers have already drawn down the water table, so the capacity of their wells has decreased. Center-pivot sprinkler systems that were installed with an adequate water supply 30 years ago may now pump only 50 percent as much water during the peak water-needs period. ASABE Center-pivot fields dot the high plains of Texas. Note that some of the fields have not been planted, possibly due to lack of adequate groundwater. tunities, the researchers share a common goal—to sustain productive irrigated agriculture. They gather annually to share their research and results at the “Tearing Down the Walls (state borders)” meeting and the Central Plains Irrigation Conference ( Northern Texas Scientists at the USDA-ARS Conservation and Production Research Laboratory (CPRL) in the Texas High Plains near Amarillo have been working on maximizing irri-gation water productivity for many years. The CPRL is near the southern end of the High Plains Aquifer, where water lev-els have been declining for many years and deep pumping depths make water expensive to extract. ASABE member Terry Howell and his colleagues at the CPRL Soil and Water Management Research Unit use large weighing lysimeters, essentially large square containers filled with soil and sitting in the ground on large scales, to precisely determine crop water requirements. Lysimeters are the standard for measur-ing water use on a daily and even hourly basis. With these large tools, the researchers can precisely measure water use and validate other, alternative ways to measure water use, such as instrumentation that measures the atmospheric ener-gy balance at the surface. They recently invited researchers from across the United States to come to their fields and com-pare their own favorite water use measurement methods with each other and with the on-site lysimeters. The techniques included instrumentation placed just above the crop canopies and satellite remote sensing imagery. As researchers gain more knowledge and confidence in their ability to measure evapotranspiration, their ability to measure and describe the effects of climatic conditions, water stress, and deficit irriga-tion also increases. One of the ways that crops respond to water stress is to close their stomates, which results in reduced water evapora-tion (evapotranspiration) and increased temperature of the crop canopy. ASABE member Steve Evett and his colleagues Subsurface drip irrigation tubing is installed at Kansas State University, Colby, Kan. RESOURCE July/August 2012 5

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