The Effect of Exchangeable Sodium and Gypsum on Surface Runoff from Loess Soil

Abstract

AbstractSurface runoff from a deep silt loam loess soil at two exchangeable sodium percentage (ESP) values (4.6 and 19.3), and the beneficial effect of industrial gypsum, were studied in field plots (of 150 m2 each) under natural rainfall conditions. The ESP of the soil was found to have a very pronounced effect on the surface runoff in spite of the fact that the final infiltration rate of the soil was affected only slightly by the ESP of the soil. The effect of ESP on the percent of surface runoff is probably through its effect on the rate of crust formation. The percent of surface runoff increased during the rainy season, for both ESP levels, because the runoff from already crusted soil was higher. However, the effect of consecutive storms depended on the degree of drying between storms. Application of industrial gypsum was found to be very effective in lowering surface runoff from the soil. Spreading the gypsum over the soil was more effective than mixing it in the upper 10 cm of soil by disk. Localization of the gypsum at the soil surface, where crust is formed, explains this effect. Gypsum application lowered the ESP of the upper 10‐cm layer for both gypsum treatments. Since the ESP of the soil in both gypsum treatments was about the same, it seems that the most important factor which controlled infiltration was the electrolyte concentration in the percolating solution.