Submitted to: Proceedings of the World Water and Environmental Resources Congress
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2007
Publication Date: 5/15/2007
Citation: Howell, T.A., Tolk, J.A., Evett, S.R., Copeland, K.S., Dusek, D.A. 2007. Evapotranspiration of deficit irrigated sorghum. In: Proceedings of the World Water and Environmental Resources Congress, May 15-19, 2007, Tampa, Florida. 2007 CDROM. Interpretive Summary: Reduction of irrigation from groundwater is vitally important in the Ogallala aquifer region on the U.S. Southern High Plains. Typically, reduced irrigation reduces crop yield and impacts the regional economy. Deficit irrigation (irrigations planned to not fully meet the crop water needs) can be used to increase the crop water productivity (yield per unit of water) commonly called “water use efficiency”. In 1993, grain sorghum was grown on two large fields each containing a weighing lysimeter (a device to precisely measure the water use by the crop). One field was fully irrigated to meet the crop water requirements (FULL) while the other field received approximately one-half the irrigation amount (DI) applied at same time both with a lateral-move sprinkler system. The DI field benefited from irrigations and rainfall before the boot growth stage (a critical growth stage in determining sorghum yield). Irrigations after the boot stage were enough to permit the crop to utilize the soil water slowly and to a deeper depth than the FULL sorghum field. The sorghum water use decreased 10% from 621 mm to 560 mm with a 48% decline in irrigation with DI. Water use efficiency for both grain and dry matter increased slightly with DI but seed mass was unaffected. DI permitted a major reduction in irrigation without a decline in crop yield by effectively using the seasonal rainfall (210 mm).
Technical Abstract: Deficit irrigation commonly is used in regions with reduced or limited irrigation capacity to increase water use efficiency (WUE). This research measured sorghum (Sorghum bicolor L. Moench) water use (ET) and yield so WUE could be determined. Two precision weighing lysimeters were used to accurately measure sorghum ET from a fully irrigated field (FULL) and a deficit irrigated field (DI; ~50% irrigation) that was irrigated by a lateral-move sprinkler system at Bushland, TX in 1993. Sorghum ET decreased 10% from 621 mm to 560 mm with a 48% decline in irrigation. WUE for both grain and dry matter increased slightly with DI but seed mass, and harvest index were unaffected. Sorghum extracted soil water mainly above 1.2 m in the Pullman soil profile if well watered, but DI sorghum extracted soil water to 1.7 m. Sprinkler DI beginning with a nearly full soil water content profile permitted the crop to better exploit the soil profile water and minimize soil water deficit effects on crop yield in a year with typical summer rainfall for Bushland (~210 mm) such that yield was not reduced by DI.