|Ayars, James - Jim|
Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2005
Publication Date: 9/2/2005
Citation: Ayars, J.E., Christen, E.W., Soppe, R.W., Meyer, W.S. 2005. The resource potential of in-situ shallow ground water use in irrigated agriculture - a review.. Irrigation Science, 2006, Vol 24: 147-160. Interpretive Summary: Irrigation uses approximately 80% of the developed water supply and will be under pressure to give up part of this supply as the demand increases for additional municipal, industrial, and environmental water supplies. This increased demand can be met without negatively impacting production through a series of actions by irrigators. They can improve water management by switching to more efficient irrigation systems and improving irrigation scheduling. An overlooked water source is shallow groundwater that is of good quality. This water source can be used by either providing subsurface drainage in areas with shallow ground water and using the drainage water for irrigation or developing management practices that induce in-situ use by crops. This manuscript reviews research describing crops that have successfully used significant quantities of water from shallow ground water. The review indicated that most plants can use shallow ground water if the root system is close enough to the water source for an extended period of time. The soil type, the salinity of the ground water, the crop salt tolerance, the length of crop growing period, and depth to the water table were identified as the major factors that determined the amount of water used by the crop. To maximize the potential use, the irrigation schedule needs to be modified to account for crop water use from the shallow ground water. Using shallow ground water to meet crop water use requirements has the potential to significantly extend water supplies.
Technical Abstract: Shallow ground water is a resource that is routinely overlooked with water management alternatives to increase the available water supply being developed for irrigated agriculture. It has the potential to provide significant quantities of water to meet crop water requirements under the proper conditions of water table depth and irrigation management. Crop water use from shallow groundwater is affected by soil water flux, crop rooting characteristics, crop salt tolerance, presence of a drainage system, and irrigation system type and management. This paper reviews these factors in detail and presents data quantifying crop use from shallow ground, and describes the existing state of the art with regard to crop management in the presence of shallow ground water. The existing data are used to determine whether in-situ crop water use from shallow ground water is suitable for a given situation. The suggested methodology uses ratios of ground water electrical conductivity to the Maas-Hoffman yield loss threshold values, the day to plant maturity relative to plant growth period, and the maximum rooting depth relative to the nearly saturated zone. The review demonstrates that for in-situ use to be feasible there has to be good quality ground water relative to crop salt tolerance available for an extended period of time. Shallow ground water availability is one area that can be managed to some extent. Crop selection will be the primary determinant in the other ratios.