Studies on a Nigerian Forest Soil

Summary The distribution of total, total organic, total inorganic, and extractable phosphorus was determined for samples from a Nigerian forest profile, and for the sand fractions and aggregate fractions of the fine earth. The soil P is accumulated in the surface soil. Below 2 in there is a marked fall in total P, reflecting a large decrease in the amount of organic P. Thereafter the total P is fairly constant down the profile. The concentration of P in the iron concretions is considerably higher than in the surrounding fine earth. In the gravel horizon, 12–30 in., over 80 per cent. of the total P at this level is immobilized in the concretions. Only the surface soil contains appreciable amounts of P soluble in acetic acid, Truog's reagent, and NH 4 F. Below 2 in., the amount of P extractable by these reagents falls sharply. There is very little Ca‐bound phosphate below 2 in. Considerable amounts of P are extracted from all horizons by 0.1 N NaOH which extracts strongly adsorbed forms of P. The clay fraction of the topsoil contains large amounts of P soluble in NaOH.