Irrigation scheduling to prevent soil salinization from a shallow water table

Abstract

The purpose of this study was to develop a model to quantify the rate of upward water movement from a shallow water table for different soils with and without plants as a function of water table depth and time; to predict electrical conductivity (EC) of the soil in a one-dimensional homogenous soil profile; and to develop a water management procedure to control soil salinity in the presence of a shallow water table. The model simulates water and solute movement from a shallow water table for a bare soil surface. Salt distribution in the soil profile, caused by a saline shallow water table, was simulated by assuming a steady state upward water movement in the absence of a crop. As water moves upward through a soil profile from a shallow water table with dissolved salts, the water evaporates at the surface, leaving the salt behind. Some of the salt moves down to a depth about 30 em by molecular diffusion. This raises the salt concentration within the top 30 cm of the soil. The model simulates crop water extraction patterns and consequently the salt distribution patterns in an irrigated soil profile for a specified root distribution. After a fallow season and the resulting salt concentration near the soil surface, the salt redistributes downward because of irrigation water application. Different leaching fractions were used in the simulations. A computer program was written called SALTCTRL (Salt Control) for the model in QBASIC language. The program was tested using two soils with different leaching fractions. The soil parameters needed for the computations were selected from the literature. Application of model results is discussed and recommendations for further research were made.