Salinity and sodicity can cause hysteresis in soil hydraulic conductivity

Soil salinization and sodification can cause severe damage to soil structure, with important implications for irrigated agriculture. Knowledge of the extent to which degradation in soil structure due to salinization and sodification is reversible, however, is still lacking. The objective of our study is to examine how the history of solute composition affects the degree of reversibility in saturated hydraulic conductivity (K_sat). We systematically investigate the effects of salinity (electrolyte concentration) and sodicity (sodium adsorption ratio) on K_sat, for three soils of varying clay content. The soil column experiments yielded hysteresis graphs, in which K_sat does not go back to its original value after initial decay. We developed indices to quantify the degree of K_sat degradation and reversibility, and found that contrary to our expectations, high susceptibility to degradation does not always correlate with low capability to rehabilitate. Measurements of soil swelling helped us discern when degradation was mainly caused by swelling or clay dispersion. Our findings underscore the need for understanding hysteresis caused by salinity and sodicity, aiming at better management of agricultural soils for sustainable long-term use.