Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2002
Publication Date: 4/7/2003
Citation: TOLK, J.A., HOWELL, T.A. WATER USE EFFICIENCIES OF GRAIN SORGHUM GROWN IN THREE USA SOUTHERN GREAT PLAINS SOILS. AGRICULTURAL WATER MANAGEMENT. 2003. V. 59. P. 97-111. Interpretive Summary: About 70% of the world's usable fresh water is used to irrigate agricultural crops. Irrigation is critical for not only maintaining the level of current food production but boosting production as well. Irrigation water supplies are declining, however, due to shrinking aquifers and increasing competition from industry and a rapidly growing population. To maintain or even increase production, agricultural producers must make more efficient use of the limited water remaining for them. Two measures of the efficiency of crop production and management systems are water use efficiency and irrigation water use efficiency. Water use efficiency relates the amount of yield (such as grain) produced to amount of water the crop used. Irrigation water use efficiency relates yield to the amount of irrigation water applied. This study evaluated how different amounts of seasonal irrigation, soil type, and climatic differences affected these water use efficiencies for grain sorghum. It found that when the growing season is very hot and dry, both water use efficiencies declined compared with what happens in a more average season. This is because the higher evaporation of water from the soil surface means less can be used by the crop. The crop then will experience water stress (which can reduce yield), because of less water and uses remaining water more rapidly because of the high temperatures. This type of climate can also reduce yield of crops grown in some soils even when there is enough water, since the amount of water needed by the crop cannot move rapidly enough through the soil to the plant roots. The study also showed how the water initially stored in the soil is an important supplement to irrigation for meeting a crop's water needs.
Technical Abstract: The ratios of economic yield: evapotranspiration, or water use efficiency (WUE), and economic yield: irrigation water application, or irrigation WUE (IWUE), help evaluate the productivity of irrigation in agricultural systems. The objectives of this research were to evaluate whether soil type, soil water use characteristics, and seasonal climatic differences affect the WUE and IWUE of grain sorghum. In 1998 and 1999, grain sorghum was grown in 0.75-m rows with 16 plants per m**-2 at Bushland, TX, in lysimeters containing monolithic soil cores of either the Amarillo, Pullman, and Ulysses soil series. Irrigation treatments in both years were 100%, 50%, 25%, and 0% replacement of ET. The difference in climatic conditions between 1998 and 1999 affected WUE, IWUE, and ET of grain sorghum, with WUE and IWUE significantly higher and ET lower in 1999 due to milder climatic conditions compared with 1998. Crops grown in the Amarillo osoil had significantly higher WUE compared with crops in the other soils, primarily due to reduced ET. Once normalized for climatic differences, yield response to ET was similar for both years. The relationship between irrigation application and yield was more curvilinear under milder climatic conditions, and more linear with higher evaporative demands. In general, IWUE declined with increasing irrigation application within each year, but was variable in some irrigation treatments, due to water stress at critical growth stages. No differences among soil types occurred in IWUE in either year, primarily due to variability among replicates.