Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 16, 1998
Publication Date: N/A
Interpretive Summary: Corn is a major irrigated crop in the Southern High Plains and has a large irrigation requirement. It is usually a fully irrigated crop because it can be sensitive to water shortages, especially at pollination. The crop water stress index (CWSI) is a technique that uses measurements of the crop surface temperature using an infrared thermometer (IRT) and atmospheric humidity data (VPD) to infer the crop water status. This study examined how the CWSI was related to crop yield, soil water, and yield components (kernel weight, kernels per unit area, and kernels per ear) across a wide range of imposed water deficits but irrigated frequently using the LEPA technology. The CWSI was found to be sensitive to crop water deficits resulting from reduced irrigation and that it would be an asset in scheduling irrigations, especially in addition to soil water measurements and/or evapotranspiration models. A CWSI value exceeding 0.33 was determined to be a level where significant yield reductions occurred from water deficits.
Technical Abstract: This study evaluated the crop water stress index (CWSI) for LEPA (low energy precision application) irrigated corn (Zea mays, L.) grown on slowly permeable Pullman clay loam soil during the 1992 growing season at Bushland, TX. The effects of six different irrigation levels (100%, 80%, 60%, 40%, 20%, and 0% replenishment) of soil water depleted from the 100% soil water replenishment treatment on corn yields and the resulting CWSI were investigated. The yield, water use, and water use efficiency of fully irrigated corn were 1.246 kg/m**2, 786 mm, and 1.34 kg/m**3, respectively. CWSI was calculated from measurements of infrared canopy temperatures, ambient air temperatures, and vapor pressure deficit values were evaluated for the six irrigation levels. A "non-water-stressed baseline" equation for corn was developed using the diurnal infrared canopy temperature measurements as Tc - Ta = 1.06 - 2.56 VPD, where Tc was the canopy temperature (øC), Ta was the air temperature (øC) and VPD was the vapor pressure deficit (kPa). Trends in CWSI values were consistent with the soil water contents induced by the deficit irrigations. Both the dry matter and grain yields decreased with increasing water deficit. Minimal yield reductions were observed at a threshold CWSI value of 0.33 or less for corn. The CWSI was useful for evaluating crop water stress in corn and should be a valuable tool to assist irrigation decision making in addition to soil water measurements and/or evapotranspiration models.