The resource potential of in-situ shallow ground water use in irrigated agriculture: a review
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Shallow ground water is a resource that is routinely overlooked when water management alternatives are being considered in irrigated agriculture. Even though it has the potential to provide significant quantities of water for crop use under the proper conditions and 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.