Role of the soil particle-size fractions in the sorption and desorption of potassium

The sorption and desorption capacities of two soils (a loamy soddy-podzolic soil and a sandy clay chernozem) were analyzed. Both the entire soils and their particle-size fractions were studied. Samples were taken from the soils of long-term field experiments with fertilizers. A 0.01 M CaCl2 solution was used as the extractant. The soil fractions < 10 mu m were found to have the maximum capacities for sorption-desorption of potassium. The soil fractions < 0.2 mu m were the most enriched with potassium. The use of kinetic methods of analysis allowed assessing the contributions of the particle-size fractions to the potassium status of soils with different degrees of fertilization. It was noted that different fertilizing systems had no effect on the rates of potassium desorption from the colloidal fraction, while appreciable differences among the different treatments were observed for the fractions of 0.2-1.0 and 1-10 mu m.