Improving effect of potassium in organic amendments on sodic soils

Abstract

ABSTRACT Sodification is a major soil problem that limits plant productivity in arid and semi-arid regions. For ameliorating sodic soils, the application of chemical amendments that can release calcium (Ca), which expels soil exchangeable sodium (Na), is the most widely accepted approach for solving this problem. However, an alternative more economical method would be desired in developing countries that have large areas of sodic soils. The goal of the present study was to examine the effectiveness of using compost to expel soil exchangeable Na. Composts made from cattle manure, rice straw, and rapeseed pomace were added to a sodic soil (Tongliao, Inner Mongolia, China) at mass ratios of 0 − 10%, and the soil was leached with water. Soil exchangeable cations in the forms of outer sphere and inner sphere complexes were then extracted successively and their concentrations determined. Changes in the soil dispersibility resulting from the addition of compost was also examined. The concentration of Na in both the outer sphere and inner sphere complexes decreased when rice straw or rapeseed pomace compost added, but this was not observed when cattle manure compost, which is abundant in water-soluble Na, was used. The amount of K in both forms increased with increasing rate of addition of each compost, suggesting that the K in the compost replaced both the Na that is adsorbed to soil by electrostatic attraction and by chemical interactions. The largest removal of Na, 73% for outer sphere complex and 93% for inner sphere complex, was attained in the case of rapeseed pomace compost, which had the largest water-soluble K/water-soluble Na ratio, at a mass ratio of 5%. The addition of compost also neutralized soil pH and reduced soil dispersion, the latter being effective in improving the physical properties of the soil.