Published online by Cambridge University Press: 27 March 2009
The phosphorus status of five Nigerian coastal plain sands was evaluated by determining the relative abundance of the various P forms and the P adsorption capacities of the soils. Total P ranged from 4460 to 1129 mg/kg. Organic P had a range of 23–232 mg/kg and formed below 30% of total P in four of the profiles but above 50% in the hydromorphic Otegbo profile. The relative distribution of the various inorganic forms was in the increasing order of residual P, active P and occluded P, except in the Onne profile in which the residual P was relatively the least abundant. The relative distribution of the active P forms was in the decreasing order of Fe-P, Al-P and Ca-P.
The adsorption capacity varied widely among the soils. The amount adsorbed from the addition of 150 mg/100 g of soil ranged from 40–2 to 86–2 mg/100 g and was related to the clay content. The adsorption at 0–3 mg/1 P in equilibrium solution ranged from 19 to 265 mg/kg. The subsoils generally adsorbed more P than the surface soils. The P requirements of the soils estimated from the sorption capacities were in the low and medium ranges.