Submitted to: Technical Conference on Irrigation Drainage and Flood Control
Publication Type: Proceedings
Publication Acceptance Date: June 3, 1998
Publication Date: N/A
Interpretive Summary: New methods of managing irrigation and drainage water are needed if irrigated agriculture is to survive and be environmentally responsible. A new technique for scheduling irrigation was tested which incorporated crop water use from shallow ground water and was found to be effective in reducing the irrigation water requirement of cotton. This means that less irrigation water is required and drainage volumes are reduced. This will improve the water quality of surface water by leaving more in the stream or lake and reducing the salt load being transported. Control of the water table by blocking the subsurface drain outlet also resulted in reduced drainage flow and increased water uptake from shallow ground water by a tomato crop. A water balance computation demonstrated that improved irrigation efficiency will have a larger effect on the reduction of drainage flow than will use of shallow ground water by a crop.
Shallow ground water in arid irrigated areas has generally been treated as a waste product of irrigation which was to be discharged into an available water course for ultimate disposal in an ocean. This practice is no longer environmentally acceptable and means need to be developed to minimize the environmental impact of uncontrolled discharge of drainage water from irrigated lands. This paper presents the results of field and theoretical studies which demonstrate methods to reduce and minimize the volume of drainage water for disposal. The field studies demonstrated the use of subsurface drip irrigation with modified crop coefficients to increase the water use from shallow ground water, and the use of control structures on drainage systems to control the depth to shallow ground water to improve the water use by the crop from shallow ground water. Application of these techniques resulted in significant use of ground water by cotton and tomato. The theoretical studies demonstrated that using new drainage design criteria will result in less drainage discharge and lower salt loads. Improved irrigation efficiency will have the largest impact on reducing total drainage discharge.