Submitted to: Journal of Irrigation and Drainage Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2000
Publication Date: N/A
Interpretive Summary: Disposal of saline subsurface drainage water is one of the major challenges facing irrigated agriculture in arid and semi-arid areas. Subsurface drainage has been eliminated on 600,000 acres of irrigated land on the west side of the San Joaquin Valley because the subsurface drainage water from this area contains potentially toxic trace elements in addition to salt. The first step in developing methods to discharge drainage water will be to reduce the volume to the least practical level through improvements in irrigation system design and management and increased water use from shallow ground water. This concept has been called source control. This paper describes research demonstrating the potential for shallow ground water use by crops through improved irrigation scheduling and managing the groundwater level with controls on the drainage system. Irrigation scheduling methods which include shallow groundwater contribution to crop water requirements resulted in cotton taking nearly 45% of its water requirement from shallow ground water. Weirs and valves installed in a subsurface drainage system were capable of controlling the water table positions across a half mile long field. This reduced the total water application to a tomato crop. These techniques combined with improved irrigation system design and management will result in a sustainable alternative for irrigated agriculture.
In-situ use of ground water by plants is one option being considered to reduce discharge of drainage water from irrigated agriculture. Laboratory, lysimeter, and field studies have demonstrated that crops can use significant quantities of water from shallow ground water when properly managed. However, most studies lack the data needed to include the crop water use into an integrated irrigation and drainage water management system. This paper describes studies which demonstrated the potential in-situ use of ground water by salt tolerant crops and the limitations. Included are results from three field studies which demonstrated management techniques needed to develop an integrated system which includes irrigation scheduling and control of the water table with structures in the subsurface drainage system. The field studies demonstrated that approximately 40 to 45% of the water requirement for cotton can be derived from shallow saline ground water. That regulation of the subsurface drainage system outflow results in increasing use of ground water by a crop. Implementation of integrated management of irrigation and subsurface drainage systems is a viable and sustainable alternative in the management of subsurface drainage water from arid and semi-arid areas only if soil salinity can be managed and if the system is profitable.