Soil water regime in economic evaluation of salinity in irrigation

Abstract

A field irrigation experiment and computer and statistical models are used to estimate the functional relationships between the total soil water suction and the man‐controlled variables, the quantity and salinity of the water, and the irrigation frequency. It is estimated that the seasonal average soil water suction S in the root zone increases with each of the variables: the irrigation interval, water salinity, and initial soil salinity. The value of S also increases with the amount of irrigation water Q at low values of Q, but decreases with Q at relatively high values of Q. Under the conditions studied, it is more efficient to use given quantities of irrigation water (from the standpoint of salinity) for changing the soil water regime rather than for leaching. An approach to the economic evaluation of the optimal combination of water quantity and salinity in the short run is outlined. This approach is based on a previous empirical estimate of the effect of water suction on yield, and on the present estimate of the functional relationships between the total soil water suction and the man‐controlled irrigation variables.