Abstract

Soil chemical forms of Phosphorus and P sorption capacities of Fincha Sugar Estate soils were studied using samples collected from luvisols, vertisols and fluvisols of the farm. P forms were sequentially extracted following standard P fractionation procedure. In sorption study, 3 g of soil sample was equilibrated with 30 ml of 0.01 M CaCl₂ containing various amounts of KH₂PO₄. Data were fitted into Langmuir and Freundlich equations. Results revealed that organic P (Po) accounted for the larger proportion of total P than total active inorganic P fraction in 66.7% of soils. The ratio of organic carbon to Po was < 200 in all soils indicating net mineralization of Po. Ca-P was dominant in luvisols and vertisols whereas Fe-P was dominant in fluvisols. P sorption data of all soils fitted well with Langmuir equation but the P sorption data of these soils were found not to fit with Freundlich equation. Langmuir adsorption maxima and external P requirement (EPR) of soils ranged from 227.3-344.8 and 63-153.8 mgkg^-1 respectively. Luvisols and vertisols which account for more than 95% of the farm had EPR values < 150 mgkg^-1 and hence they were classified as low P sorbing soils. This implies that high P sorption is not P limiting factor in the estate. The result further indicates that current P fertilizer application rate of 30 kg P ha^-1 being practiced across all soil types of the farm needs to be revised after validating the EPR values estimated in this study for each soil both in greenhouse and in the field at Fincha Sugar Estate.

Key words: P fractions, P sorption, Langmuir equation, Freundlich equation.