Determinants of swelling and dispersion in reducing drainage in soils affected by sodification

Soil sodification commonly occurs in irrigated soils of arid and semi-arid regions, resulting in serious decreases in productivity. Because an apparent consequence of sodic soils in farmlands is the significant deterioration of drainage capacity, the impacts of different types of water, such as irrigation water, groundwater, and rainfall, on soil drainage need to be assessed for sustainable land management. We investigated changes in soil saturated hydraulic conductivity (HC) under different salt treatments by separating the effects of swelling and dispersion. The salt treatments were conducted at different salt compositions (SAR∞, SAR10, SAR0; SAR=Na/(Ca/2) 1/2 (cations: mol c L -1 )) and concentrations (0.05, 0.01, 0.001 N) on Indian soil (sandy clay loam). The soil cores were continuously leached with each treatment solution, and the HC was plotted against the cumulative amount of percolating solution. Our results support the existing findings that dispersion is triggered at concentrations below the critical coagulation concentration (CCC), which further varies with swelling and reflects the degree of sodification in a single mineralogy. We further revealed that the CCC could vary without changing the level of swelling; thus, whether or not dispersion occurs could be controlled independently of the determinants of swelling.