Effect of water quality on the leaching of potassium from sandy soil

Abstract

When potassium (K +) fertilizers are applied to soil, K + is subject to displacement through the soil profile. More generally, the application of K + fertilizers to sandy soils with low clay content and small buffer capacity, in which K + does not interact strongly with the soil matrix, results in localized increases in K + concentration in the soil solution. Losses of K + depend on the concentration of calcium (Ca 2+) as a competing ion in the leaching water and the amount of water that passes through the soil. In this study, we examined the adsorption and movement of applied K + in columns of sandy soil. Glass tubes, 4.8 cm in diameter and 40 cm in length, were packed with either native soil or Ca 2+-saturated soil. The resulting 10-cm-long column of soil had a bulk density of 1.65 g cm −3. Native soil was leached with distilled water and CaCl 2 solutions of various concentrations. In the Ca 2+-saturated soil, a pulse of K + was leached with CaCl 2 solutions of various concentrations or distilled water. Increasing the CaCl 2 concentration from 3 to 15 m m resulted in earlier breakthrough, a higher peak concentration of K +, and greater amounts of leached K +. The breakthrough curve for K +, when leached with distilled water, showed very low concentrations and was more delayed than the other treatments. In Ca 2+-saturated soil, the amount of K + leached increased as Ca 2+ concentration increased, with up to 54% of the added pulse K + being removed from 10 pore volumes (Pv) (387 mm) of 15 m m CaCl 2. The presence of Ca 2+ in irrigation water and soil minerals able to release Ca 2+ is important in determining the amount of K + leached from soils. Large amounts of K + are leached from soils in areas where crops are irrigated with water that contains significant concentrations of Ca 2+ and other cations.