|Ayars, James - Jim|
Submitted to: Agricultural Water Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/22/2006
Publication Date: 7/4/2006
Citation: Ayars, J.E., Christen, E.W., Hornbuckle, J.W. 2006. Controlled drainage for improved water management in arid regions irrigated agriculture. Agricultural Water Management 86 (20060 128-139. Interpretive Summary: Irrigated agriculture provides 40% of the world food supply on approximately 17% of the cropped land and is expected to provide additional food in the future and elimination of irrigated agriculture is not a viable option. There are environmental consequences associated with the need to provide subsurface drainage to sustain irrigation. Drainage water from irrigated agriculture oftentimes contains nitrate, salt, and toxic elements that excessively contaminant surface water. Previously, subsurface drains were allowed to run continuously and discharge salts in excess of what is needed to sustain irrigation by maintaining the salt balance in the crop root zone. This paper describes new design and management required for subsurface drains in irrigated agriculture that will result in the irrigation and drainage systems being operated as a water management system. The initial step will be to improve the irrigation system design and operation and then design the drainage system based on the improved irrigation system type and management. The drainage system will include controls that will enable regulation of the drainage flow and water table position. New design criterion for the mid-point water table depth is suggested that will allow the water table to rise closer to the soil surface. The effect of implementation of these improvements will be to reduce the total flow from the system and thus the salt load, and reduce the total irrigation water requirement. Field studies have shown that implementing drainage control has reduced the drainage discharge and a salt load and total irrigation water requirement. Research has also shown that salinity accumulation in the crop root zone can be managed through pre-plant irrigation, rainfall, and seasonal irrigation. Implementation of these practices will extend the available water supplies and reduce the environmental impact of irrigation.
Technical Abstract: In arid regions, controlled drainage is the next step towards improving water management in irrigated agriculture and reducing the environmental impacts of subsurface drainage flow. Controlled drainage has been practiced in humid areas for a long time. In this paper traditional subsurface drainage system design procedures are described, followed by alternative design criteria and suggestions for system design to include control structures that enable drain system management. The suggested changes include reducing the installation depth of laterals, accounting for crop water use from shallow ground water in the design, relaxing the mid-point water depth requirement. Active control of drainage systems in arid irrigated regions is a developing concept that is currently being evaluated around the world. Research in the U.S. and Australia has demonstrated that water tables in irrigated areas can be effectively controlled with various types of structures. Control has resulted in reduced volume of drainage water and salt loads. Salt accumulation in the root zone is a consideration in adopting controlled drainage, but other research has demonstrated that it is possible to manage salt accumulation through careful water management.