Phosphate Sorption Parameters in Relation to Phosphate Desorption in Acid Soil

The relationship between the phosphate sorption indices and phosphate desorption by Bray P1. Bray P2, Olsen and Mehlich extractants was studied in 15 acid Inceptisols of Sikkim. The amount of phosphate extracted increased with an increasing amount of sorbed phosphate, irrespective of extractants used. The soils which had the higher P sorption capacity (b) and surface affinity constant (k) desorbed lesser amount of sorbed phosphate by different extractants used than those having lower P sorption indices. The P sorption capacity, sorption energy constant and maximum buffering capacity (mbc=b.k) were negatively and significantly correlated with desorption. The fraction of the phosphate sorption capacity (% saturation) covered with added P sorbed on soil surface controlled highly the desorption of P by different extractants. The amount of sorbed P fixed (non-mobile) against Bray P1 (0.03N NH4F + 0.025N HCl) was highly related to the fixed P by other extractants, reflected that P fixed against Bray P1 or vice versa could be determined. The P sorption indices were also highly andpositively related to the P fixed by soil, indicated the positive role of P sorptionfor its immobilization.