Effect of Cation Species on the Desorption of Phosphorus in Soils Treated with Carbonate

Three‐month incubation of soils with K 2 CO 3 raised the pH about the same as did an equivalent amount of CaCO 3 but was substantially more effective in enhancing the water solubility of P (4–14‐fold at the solution to soil ratio of 60:1). In the K 2 CO 3 ‐treated samples, the KCl added to achieve a 25% increase in ionic strength caused an 11–44% drop in the water‐soluble P. However, if the water to soil ratio increased, the P desorption in the CaCO 3 amended samples approached that in the K 2 CO 3 ‐treated soils, and the KCl‐induced reduction in water‐soluble P diminished. These responses to changes in the extraction ratio were taken to indicate that the cation species of the liming material and the ionic strength in the matrix solution affected the rate more so than the absolute quantity of P desorption. The significance of these factors under field conditions was discussed.