Soil salinity modeling over shallow water tables. II: Application of LEACHC

Root zone salinity is one of the major factors adversely affecting crop pro duction. A saline shallow water table can contribute significantly to salin ity increases in the root zone. A soil salinity model (LEACHC) was used to simulate the effects of various management alternatives and initial conditi ons on root zone salinity, given a consistently high water table. The impac t of water table salinity levels, irrigation management strategies, soil ty pes, and crop types on the accumulation of salts in the root zone and on cr op yields was evaluated. There were clear differences in soil salinity accu mulations depending upon the depth and salinity of the water table. In gene ral, increasing water table depth reduced average soil profile salinity, as did having lower salinity in the water table. Among the four irrigation st rategies that were compared, the 14-day irrigation interval with replenishm ent of 75% of 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 of salt accumulation. Soil type and crop type had minimal or no impact on soil salinity accumulation. Unde r all conditions, soil water average electrical conductivity increased duri ng the 3-year simulation period. This trend continued when the simulation p eriod was extended to 6 years. Under the conditions shown to develop the hi ghest average soil salinity (high water table, low irrigation), an annual p resowing irrigation of 125 mm caused a nearly 50% reduction in soil salinit y at the end of the 6-year simulation period, as compared with the soil sal inity given no presowing irrigation.