Infiltration of Water into Nonuniform Soil

A simplified procedure for calculating infiltration into soil of nonuniform water content or hydraulic conductivity, or both, is presented. The procedure is based on the Green and Ampt model of piston flow. Input data consist of the difference in water content before and after wetting, the hydraulic conductivity after wetting, and the water entry value of the soil. Techniques for measuring these parameters in the field are briefly described. The procedure is applied to calculate infiltration-time relationships for flood irrigation of a coarse-textured and a fine-textured soil, and to evaluate the effect of nonuniform inundation time on irrigation efficiency. The results show that the usual recommendation of allowing an inundation-time difference of not more than 25% of the time required for the desired amount of water to infiltrate into soil can give irrigation efficiencies of 90% or more. Thus, larger differences in inundation time can be allowed in practice, particularly if the hydraulic conductivity of the soil decreases with depth.