|Ayars, James - Jim|
Submitted to: Journal of Irrigation and Drainage Engineering
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/14/2000
Publication Date: N/A
Citation: Interpretive Summary: Root zone salinity is a problem for sustaining arid irrigated agriculture throughout the world. Both the United States and Pakistan are faced with the problem of managing irrigation in the presence of shallow saline water tables. The rate of salinity accumulation in the root zone is a function of the depth of the water table, the soil type, the salinity of the ground water, and the crop. In a companion study the LEACHC model was validated for use in evaluating the effects of water table depth and salinity on salt accumulation in the root zone. Irrigation strategies for managing salt accumulation were evaluated as was the effect of soil type and crop. Simulation results demonstrated that as water became more saline a deeper water table was needed to maintain yields. Pre-plant irrigation for leaching was found to be necessary to maintain sustainability. Pre-plant irrigation in fallow periods is a very common practice in many arid irrigated areas. It serves to leach the root zone and replenish the soil water.
Technical Abstract: Root zone salinity is one of the major factors adversely affecting crop production. A saline shallow water table can significantly contribute to salinity build up in the root zone. A soil salinity model (LEACHC) was used to simulate the effects of various management alternatives and initial conditions on root zone salinity, given a consistently high water table. The impact of water table salinity levels, irrigation management strategies, soil types, and crop types on the accumulation of salts in the root zone and on crop yields was evaluated. There were clear differences in soil salinity depending upon the depth and salinity of the water table. Among the four irrigation strategies which were compared, the 14 day irrigation interval with replenishment of 75% evapotranspiration (ET) resulted in the lowest soil salinity. With a 4 day interval and 50% ET replenishment, a wheat yield reduction of nearly 40% was predicted after three years accumulation. Soil type and crop type had minimal or no impact on soil salinity. Under all conditions, soil average electrical conductivity increased during the 3-year simulation. This trend continued when the simulation period was extended to six years. Under the conditions shown to develop the greatest soil salinity (high water table, low irrigation), an annual pre-sowing irrigation of 125 mm caused a nearly 50% reduction in soil salinity at the end of the six-year simulation period.