Submitted to: Irrigation Association Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 15, 2010
Publication Date: December 5, 2010
Citation: Oshaughnessy, S.A., Evett, S.R., Colaizzi, P.D., Howell, T.A. 2010. Automatic irrigation scheduling of grain sorghum using a CWSI and time threshold. In: Proceedings of the 5th Decennial National Irrigation Symposium, December 5-8, 2010, Phoenix, Arizona. Paper No:IRR10-9011.2010 CDROM. Interpretive Summary: Scheduling irrigations based on plant feedback is a tool that can help improve water use efficiency by irrigating only when the crop needs water. This study investigates the use of the crop water stress index (CWSI) over a 24-hour period of time as an irrigation trigger for an early variety grain sorghum hybrid and investigates the impact of deficit irrigation on crop yield. The field was divided into six pie-shaped zones, of which three were irrigated automatically using the CWSI and three were irrigated based on information from weekly neutron probe readings. Each zone had four irrigation treatments and two replications. The yields from the automatically irrigated treatment plots receiving the highest level of irrigation compared well to those manually irrigated at the same treatment level. Irrigation water use efficiency was similar between irrigation methods in the 55% and 30% treatments, but significantly greater in the 80% automatically controlled treatments. These preliminary results indicate that the CWSI and time threshold have the potential to benefit farmers in scheduling irrigations. Further research is required to investigate its stability over different growing seasons and using different crops.
Technical 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 less than 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.