Abstract
The alluvial entisols at Los Diamantes, Costa Rica contained relatively large amounts of phosphorus. However only small percentages of this phosphorus were extractable. Most of the total phosphorus was probably unavailable to plants. Laboratory tests showed that lime did not affect the relative proportions of extractable soil aluminium, iron, and calcium phosphates. Most of the phosphorus retained was in the aluminium form. The soils had high phosphorus retention capacities. Phosphorus retention by the subsoils, particularly was increased by lime treatments, possibly because of the large surface of aluminium hydroxide formed. In soils from two glasshouse experiments, it was found that more aluminium phosphate than iron and calcium phosphates was formed by incorporating phosphorus into the soil, especially at high phosphorus rates. Lime favoured aluminium phosphate formation but had a negligible effect on iron and calcium phosphate. A larger portion of the applied phosphorus was in Iess soluble forms when the soil was unlimed. Soil organic phosphorus was markedly lower at the end of a seven month period than it had been before the experiment was begun.
