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United States Department of Agriculture

Agricultural Research Service

Research Project: IRRIGATION MANAGEMENT AND AUTOMATION FOR INCREASED WATER USE EFFICIENCY

Location: Soil and Water Management Research

Title: Evapotranspiration of deficit irrigated sorghum and winter wheat

Authors
item Howell, Terry
item Tolk, Judy
item Evett, Steven
item Copeland, Karen
item Dusek, Donald - USDA-ARS (COLLABORATOR)

Submitted to: Irrigation and Drainage International Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 30, 2007
Publication Date: October 3, 2007
Citation: Howell, T.A., Tolk, J.A., Evett, S.R., Copeland, K.S., Dusek, D.A. 2007. Evapotranspiration of deficit irrigated sorghum and winter wheat. In: Clemmens, A.J., editor. USCID Fourth International Conference on Irrigation and Drainage. The Role of Irrigation and Drainage in a Sustainable Future, October 3-6, 2007, Sacramento, California. p. 223-239. 2007 CDROM.

Interpretive Summary: Areas or regions like the Southern High Plains often have reduced irrigation capacity requiring deficit irrigation. Deficit irrigation is designed for planned soil water deficits. These experiments measured crop water use (ET) from winter wheat in 1991-92 when irrigations were stopped at the jointing stage so irrigation water might be switched to summer crops. In 1993, sorghum irrigation rate was reduced by 50% to simulate a lower irrigation capacity. Both crop ET rates were compared to fully-rrigated companion fields. All irrigations were applied by sprinkler irrigation. Crop ET was measured with precise, large weighing lysimeters (closed containers that permit the water volume to be measured accurately). One field was fully irrigated to meet the crop water requirements (FULL) while the other field received approximately one-half the irrigation amount (DI) for the sorghum or no irrigations after jointing for the wheat. Wheat ET was decreased by 20% from 849 to 677 mm with a 76% decline in irrigation. Sorghum ET decreased 10% from 621 mm to 560 mm with a 48% decline in irrigation. Water use efficiency (productivity per unit of water) of sorghum for both grain and dry matter increased slightly with DI but seed mass and harvest index were unaffected. DI irrigated wheat extracted soil water to a depth of 1.7 m in the Pullman soil with some apparent root extraction to the 2.3-m depth. 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 of sorghum 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. Cutting off winter wheat irrigation in early spring with a near-full soil water profile at jointing, permitted the wheat crop to fully exploit the soil water reservoir when rainfall was normal.

Technical Abstract: Deficit irrigation commonly is used in regions with reduced or limited irrigation capacity to increase water use efficiency (WUE). This research measured winter wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L. Moench) water use (ET) and yields so WUE could be determined. Two precision weighing lysimeters were used to accurately measure the crop ET from fully irrigated (FULL) fields and deficit irrigated (DI) fields. The DI wheat was an irrigation cutoff at the jointing growth stage as might be used if available irrigation water was being shifted to summer crops while the sorghum DI used a reduced irrigation rate (~50% FULL irrigation) as might occur with a lower irrigation capacity. Both crops were irrigated by a lateral-move sprinkler system at Bushland, Texas. Wheat ET was decreased by 20% from 849 to 677 mm with a 76% decline in irrigation. Sorghum ET decreased 10% from 621 mm to 560 mm with a 48% decline in irrigation. WUE of sorghum for both grain and dry matter increased slightly with DI but seed mass and harvest index were unaffected. DI irrigated wheat extracted soil water to a depth of 1.7 m in the Pullman soil with some apparent root extraction to the 2.3-m depth. 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 of sorghum 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. Cutting off winter wheat irrigation in early spring with a near-full soil water profile at jointing permitted the wheat crop to fully exploit the soil water reservoir when rainfall was normal.

Last Modified: 4/16/2014
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