Phosphorus in Sierra Leone soils

Abstract

Variation in amount of extractable and total P of surface soils over soil parent material, survey area, and physiography is appreciable. The greatest variation in total P is with respect to soil parent material. Only a very small proportion of total P is extractable. Maximum amount of total P and Bray Pl are present in the surface horizons. Organic P and iron P account for a large percentage of total P. Calcium P tends to disappear in the more highly weathered soil types. Adsorption capacity for P is high; unlike the buffer capacity, it is much higher in a CaCl2 system than in a water system. For finely ground normally weathered soil samples, the rate of loss of P from the bathing solution is fairly low after 24h of continuous shaking. Part of the soluble P applied to soils become non-extractable in a few weeks. Parameters that have been used for expressing P adsorption capacity are the Langmuir adsorption maximum, which because of the presence of more than one kind of adsorbing surface in Sierra Leone soils is tedious to use, a single point adsorption index and P adsorbed at a standard equilibrium P concentration.