Effect of Liming on Phosphate Sorption Characteristics of Some Acid Soils

The effect of liming induced pH changes on P sorption of three acid soils, two of them dominant in kaolinite and the other in illite, was evaluated. Different background electrolytes were used to elucidate the mechanism of P sorption in limed soils. The quantity of P sorbed on incubation with different rates of lime varied between the soils depending upon the amounts of clay, nature of clay, free oxides and hydrous oxides of Fe and exchangeable Al³⁺. In general, P sorption followed the trend: Uchagaon > West Godavari> Khudiwani. The unusually high P sorption by Uchagaon soil might be attributed to very high content of kaolinite dominant clay. In both West Godavari and Khudiwani soils, P sorption increased very slowly with lime rate up to 100 per cent L.R. Eqv., beyond which P sorption increased very sharply. A comparison of the amount of P sorbed in different background electrolytes showed that all three soils sorbed highest amount of P in 0.01 M CaCl₂ followed by 0.01 MKCl and water. The higher amount of P sorbed in KCI than in water indicates that Al³⁺ exchanged from interlayer position and its polymer formation with increase in pH might have played a key role in P sorption of limed soils.