Predicting Optimum Depth of Profile Modification by Deep Plowing for Improving Saline‐Sodic Soils

A previously developed procedure for predicting the effect of mixed‐salt solutions on soil hydraulic conductivity (HC) was used to predict the relative hydraulic conductivity (RHC) of separate soil horizons from saline‐sodic soils, using a standard low‐salt solution following a standard high‐salt solution at a fixed exchangeable‐sodium level. These values were then used to predict the RHC of mixtures of the same horizons simulating profiles modified to various depths by deep plowing. Weighting RHC values for individual horizons by the depth fraction of each horizon in the soil mixture provided RHC values of proper magnitude, except when large proportions of calcareous subsolum material were incorporated into the mixture. Results were improved by multiplying calculated RHC values for each soil mixture by the initial HC of the mixture. This corrected for the filling of conducting pores in more permeable horizons by smaller particles from less permeable horizons during the mixing process (analogous to particle dispersion and pore sealing during the leaching of saline‐sodic soils). Soil constants determined for the mixed soils permit the prediction of the response of these soils to any other exchangeable sodium levels or soil solution concentrations of interest. Results were consistent with lysimeter and field plot observations on the same soils, including deep plowing trials.