IRRIGATING FIELD CROPS IN THE PRESENCE OF SALINE GROUNDWATER

Authors: Ayars, James; Schoneman, Richard

Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2006
Publication Date: 6/1/2006
Citation: Ayars, J.E., Schoneman, R.A. 2006. Irrigating field crops in the presence of saline groundwater. Journal of Irrigation and Drainage. Vol 55: 265-279.

Interpretive Summary: Irrigating crops in the presence of saline ground water presents unique opportunities and challenges. As the world demand for water increases, it is incumbent on agriculture to maximize the use of water of all qualities. Traditional irrigation and drainage water management in saline environments was designed to provide leaching of salt from the root zone and the discharge of saline drainage water in an uncontrolled fashion. This practice is no longer acceptable and management options were developed to maximize the use of water of all qualities and to reduce the subsurface drainage discharge volume to a minimum. This paper describes the integrated management of irrigation and drainage systems in saline soil environments to reduce total drainage flow without reducing crop yields. Methods used include using saline drainage water for supplemental irrigation, increasing in-situ crop water use of ground water, installing control structures on a subsurface drainage system to control the water table position and reduce drainage flow. In a field without subsurface drainage crop production was sustained using subsurface drip irrigation which maintained yields and reduced deep percolation to the ground water. Salt in the root zone is effectively managed using pre-plant irrigation in areas with and without subsurface drains.

Technical Abstract: In agriculture there are opportunities to improve irrigation efficiency by better management of existing systems, changing to more efficient systems, and using poor quality water as a substitute for the high quality water. An integrated irrigation and drainage water management strategy is developed using research that irrigated crops with a variety of irrigation systems and water qualities in the presence of shallow saline ground water. Irrigation systems used include furrow irrigation, surface and subsurface drip irrigation and the crops included alfalfa, wheat, cotton, sugar beet, and tomato. The first study demonstrated that saline water could be used in conjunction with good quality water to extend the available water supply and reduce the total drainage volume. Wheat yields were reduced as a result of using the saline water while the cotton and sugar beet yields were unaffected. Root zone salinity was effectively managed through winter rainfall and pre-plant irrigation but boron accumulation in the soil profile was a problem in after 5 years of operation. There was significant in-situ use of water by cotton in the furrow irrigated plots resulting from partial control of the water table. The second project evaluated irrigation management of subsurface drip and furrow systems in tomato and cotton production in the presence of shallow ( 1- 2 m deep) saline (6-9 dS/m) ground water. In one year cotton extracted approximately 40% of the 640 mm requirement from shallow ground water. The results also demonstrated that salt in the root zone can be effectively managed through pre-plant irrigation without the presence of a drainage system. Yields of both crops were increased with the use of subsurface drip irrigation and the use of crop coefficients that included in-situ crop water use increased crop water use from saline ground water. A third project evaluated the potential for managing the water table position using controls on the subsurface drainage laterals as a means to promote in-situ crop water use. Results demonstrated that the water table can be effectively managed without adverse effects on soil salinity or crop yield. In-situ use by the crop was increased as a result of the water table controls. The combined results of these and other projects are the basis for a water management system that incorporates the active management of both irrigation and subsurface drainage systems to maximize water use efficiency in irrigated agriculture by improved irrigation scheduling and reuse of saline drainage water.