2009 Annual Report
1a.Objectives (from AD-416)
Determine methods for improved quantification of evapotranspiration (ET) and crop coefficients under all constraints in order to improve irrigation scheduling and water use efficiency. Develop remote sensing technologies and tools designed for improved prediction of crop water use and water stress at field and watershed spatial scales. Develop, test, and implement feedback systems for spatially and temporally variable irrigation application of water and nutrients, and develop, test and implement improved sensors for soil water content and plant stress. Develop and validate remote sensing technologies and procedures to enhance spatially and temporally variable crop water status feedback systems for use in variable rate irrigation systems. Quantify and improve crop water use efficiency in dryland/irrigated cropping systems in relation to tillage, irrigation, and crop management practices.
1b.Approach (from AD-416)
Research approaches include determinations of crop water use by soil water balance techniques (weighing lysimeters and neutron scattering methods) in practically all experiments, which include variations in irrigation method (subsurface drip at several depths and spacings, sprinkler, and low energy precision application or LEPA), irrigation amount (full and two to three levels of deficit), tillage (no-tillage, conventional, strip till, etc.), and/or crop and crop rotation, including rotation between irrigated and dryland cropping. Automatic irrigation systems based on sensing of crop status are designed/engineered and tested for ability to control crop water use efficiency and yield, thus reducing management expense (time and effort) while allowing management to control irrigation for best profitability and optimum water use. Key in this effort is evaluation and design of new crop and soil water status sensors. Remote sensing approaches to water use prediction are expected to improve energy balance modeling methods to make them useful for managers at farm, irrigation project, and watershed scales, and for policy makers.
The research unit led a multi-institutional evapotranspiration (ET) remote sensing project at the laboratory in 2008 and data analysis continued in 2009. The project, named Bushland Evapotranspiration and Agricultural Remote Sensing Experiment 2008 (BEAREX08), involved ARS researchers from four laboratories and scientists from four universities. Aircraft measured water and carbon dioxide fluxes at different altitudes over the laboratory fields and took infrared and real color images to provide more detailed and accurate data than that obtained from satellite images. ET ground truth was provided by a network of four large weighing lysimeters and numerous neutron probe soil profile water content measurement locations. Ten eddy covariance and three Bowen ratio ET flux towers obtained data at intermediate scales. Both irrigated and dryland cotton crops were studied, and data were collected under full and three deficit irrigation levels and using manual and automated irrigation systems. A companion study investigated spray, SDI, and low energy precision application (LEPA) irrigation systems. Preliminary data indicated that cotton lint yield was on average greatest under SDI followed by LEPA. Subsurface drip also resulted in greater early season soil temperatures, which is important for germination and early growth of cotton in a thermally limited environment.
Soil water sensors for down-hole sensing of soil profile water content were designed and tested in a collaborative effort between the Bushland and Lubbock ARS laboratories. Three alternative sensors were field tested during the BEAREX08 project, yielding knowledge about temperature interferences and calibration challenges for electromagnetic sensors.
Corn germination, grain yield, water use efficiency, and early season soil water near the surface were measured to evaluate alternative subsurface drip irrigation (SDI) designs. Preliminary data indicate that germination was not greatly impacted by different drip designs due to timely early season rainfall; however, grain yields were numerically greater for drip laterals buried at 23 cm compared with those buried at 15 and 30 cm.
Sunflower water use and yield were studied in four soils using weighing lysimeters and full and deficit irrigation treatments. Sunflower grown in two sandy soils produced larger yields with less water compared with sunflower grown in clay and loam soils. Averaged across soil type, sunflower grown with 25% less water than the fully irrigated crop produced only 5% less yield, which suggests that deficit-irrigated sunflower can sustain yields while conserving valuable irrigation water resources.
Under the subordinate project number 6209-13000-012-04S, the Texas High Plains Evapotranspiration Network (TXHPET) (http://txhighplainset.tamu.edu) delivered irrigation scheduling information to irrigated producers daily in FY09, with a large increase in usage due to high energy prices. Data were used by 20 federal and state agency research and extension projects for research, meteorological modeling inputs, crop modeling, irrigation scheduling and irrigation management related teaching purposes.
Cotton Grows Better in Sandier Soils in Cooler Regions with Limited Water: Cotton's ability to produce large yields is limited by short growing seasons in the High Plains of the Great Plains. Scientists with the USDA-ARS Soil and Water Management Research Unit, Bushland, Texas, found that the early season warmth in sandy soil resulted in greater early season growth, which is especially important for crop root development. After being irrigated, sandy soil warms easily, unlike silts and clays that require more heat to warm them to temperatures that promote growth. This early season advantage results in larger yields and more efficient use of limited irrigation water. To achieve the largest yields with the least amount of water, cotton should be grown in sandy soils in the High Plains of the Great Plains in most years.
Refined Model More Accurately Calculates Row Crop Water Use in the Windy Southern Great Plains: Crop water use can be calculated from local to regional scales using computer models that are driven by satellite and weather measurements. The two-source energy balance model is one such model that has been tested in humid, less hot and windy regions where crop canopies usually covered the entire soil surface, but has not been tested for the semiarid hot and windy High Plains, where row crops often do not completely cover the soil. Scientists with USDA-ARS Soil and Water Management Research Unit at Bushland, Texas, improved the two-source energy balance model and tested it for these conditions, including new row crop submodels designed to partition sunshine between the vegetation and soil and for estimating the proportion of vegetation and soil appearing in a radiometer field of view. The new submodels significantly improved the accuracy of crop water use calculations using remote sensing technology, which is key for widespread effective management of water resources.
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Tolk, J.A., Howell, T.A. 2008. Field water supply: Yield relationships of grain sorghum grown in three USA Southern Great Plains soils. Agricultural Water Management. 95(12):1303-1313.
Kang, S., Payne, W.A., Evett, S.R., Robinson, C.A. 2009. Simulation of winter wheat evapotranspiration in Texas and Henan using three models of differing complexity. Agricultural Water Management. 96(1):167-178.
Evett, S.R., Mazahrih, N., Jitan, M.A., Sawalha, M.H., Colaizzi, P.D., Ayars, J.E. 2009. A weighing lysimeter for crop water use determination in the Jordan Valley, Jordan. Transactions of the American Society of Agricultural and Biological Engineers. 52(1):155-169.
Heng, L., Hsiao, T., Steduto, P., Evett, S.R., Howell, T.A., Raes, D., Fereres, E. 2009. Validating the FAO AquaCrop model for irrigated and water deficient field maize. Agronomy Journal. 101(3):488-498.
Tolk, J.A., Howell, T.A. 2009. Transpiration and yield relationships of grain sorghum grown in a field environment. Agronomy Journal. 101(3):657-662.
Colaizzi, P.D., Gowda, P., Marek, T.H., Porter, D.O. 2009. Irrigation in the Texas High Plains: A brief history and potential reductions in demand. Journal of Irrigation and Drainage. 58(3):257-274.
Evett, S.R., Tolk, J.A. 2009. Introduction: Can water use efficiency be modeled well enough to impact crop management? Agronomy Journal. 101(3):423-425.
Tolk, J.A., Evett, S.R. 2009. Lysimetry versus neutron moisture meter for evapotranspiration determination in four soils. Soil Science Society of America Journal. 73(5):1693-1698.