Hydraulic conductivity of calcareous soils as affected by salinity and sodicity. II. effect of gypsum application and flow rate of leaching solution

Abstract

Saline‐sodic irrigation water, coupled with low annual rainfall and high evapotranspiration in the arid and semi‐arid regions have resulted in accumulation of soluble salts in the soil solution and of cations (especially sodium ions) on exchange sites, which can alter the structure and, consequently, affect the soil hydraulic conductivity (HC). Among the different factors, the amount of gypsum applied and the flow rate of leaching solution are major factors influencing the HC of the soil in the presence of saline sodic solutions. The study was initiated to improve the understanding of swelling and dispersion processes (as two major mechanisms responsible for reduction in HC) in response to saline‐sodic conditions, in particular, the role of gypsum application and the flow rate of leaching solutions. The study was conducted in a series of two leaching experiments. In the first set, different rates of gypsum (i.e., 0, 10, 20, and 30 tons ha‐1) were mixed with 4 soil samples and leached with a saline‐sodic solution of concentration of 100 meq (NaCl+CaCl2)L‐1 with sodium adsorption ratio (SAR) 20 and the base flow rate (BFR) of 15 mL min‐1. In the second set of experiments, the same soils treated with the same gypsum level and the same leaching solutions as in the first set, but leached with the BFR of 5 mL min‐1 instead of the BFR of 15 mL min‐1. In general, the gypsum application modified the suppressing effect of salinity and sodicity on the HC values of the tested soils, and the effects were more pronounced for higher rates of gypsum applied. However, increase in the BFR from 5 to 15 mL min‐1, significantly masked this recovering effect of gypsum application, and the effect was reflected in both swelling and dispersion processes.