ABSTRACT
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Low availability of phosphorus is a major constraint on agricultural productivity in highly
weathered tropical soils. Such soils have a significant capacity to sorb large amounts of
phosphorus, taking them out of the soil solution. This limits the availability of inorganic
phosphorus for plants, whether it is already contained in the soil or added as fertilizer.
Further, some tropical soils contain only small amounts of total phosphorus, with
a relatively large proportion of this present in organic forms. This makes biological
