Automatic Irrigation Scheduling of Grain Sorghum Using a CWSI and Time Threshold

Abstract

The crop water stress index (CWSI) has been investigated extensively as a quantification of plant water stress and a threshold to time irrigations. Most studies have calculated this thermal-based index by taking instantaneous measurements or by averaging values over a short period of time, usually near midday. Although useful for quantifying stress, measurements over a short period of time have not been particularly stable. This study was conducted to compare the yield response and water use efficiencies of a short-season hybrid grain sorghum obtained from automatic irrigations triggered by a CWSI and time threshold versus those obtained from manual best-practice irrigation scheduling. Irrigation amounts of 80%, 55%, 30% and 0% of full irrigation were applied. Grain yields across the 80% and 0% treatments were not significantly different between manual and automatic irrigation control methods. The only significant difference in water use efficiency between irrigation control methods occurred in the 30% treatment plots where the largest variability in the initial soil water profile existed. Irrigation water use efficiency was similar between irrigation methods in the 55% and 30% treatments, but significantly greater in the 80% automatically controlled treatments at p = 0.05. These results indicate that the CWSI and time threshold index has the potential to be utilized as a tool for deficit irrigation scheduling of grain sorghum. Further research is required to investigate its stability over different growing seasons.