Prediction of cation distribution, gypsum requirement, and infiltration rate in dynamic soil-water systems

Abstract

A computer program for prediction of the cation distribution resulting from irrigation of a layered soil was prepared. Half scale models of a ten-layer soil profile were constructed from chemically unaltered Qua Loam aid Qua Silt Loam soil samples A synthetic Colorado River water was the percolating solution. Comparison of predicted and experiments], results showed satisfactory agreement. A gypsum requirement prediction loop was inserted into the program. This loop predicted the quantities necessary to reduce the exchangeable sodium percentage of a given layer to a desired level. Intensive experimental investigation proved this method of prediction accurate. The dependence of the hydraulic conductivity of a soil upon its exchangeable sodium percentage was taken advantage of in an attempt at prediction of infiltration rates during irrigation. Despite elaborate precautions against interference by extraneous factors, the attempt was not successful. The source of error was probably the formation of a soil film of high exchangeable sodium percentage at the interface between the soil column and the percolating solution.