Variation of Forms of Phosphorus in the Sandy Soils of Coastal Fynbos, South-Western Cape

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Abstract
(1) The different soils at a coastal fynbos site in the south-western Cape, South Africa, consist of wind-blown sand and were compared for total, Bray No. 2 and resinextractable phosphorus, organic matter, pH, bulk density and iron content. (2) Resin-extractable phosphorus and iron content varied significantly between the soils. (3) A decrease in iron content followed a weathering series of soils: Hutton > Griffin > Clovelly > Constantia > Lamotte. (4) Total, Bray No. 2 and resin-extractable phosphorus of the Clovelly soil varied with depth and seasonal variations occurred at the soil surface. (5) Organic phosphorus in the Clovelly soil was determined using three methods and at the soil surface values ranged from 28% to 60% of the total phosphorus content. (6) The major inorganic phosphorus fraction in the Clovelly soil was iron-bound. (7) Resin-extractable phosphorus contents were lower in the rhizosphere zones of a restioid and an ericoid root system than in the rhizosphere regions of Proteaceae growing in the same soil. (8) The low phosphorus status of coastal fynbos soils of aeolian origin is probably associated with low total phosphorus content and is similar to the Australian heathland soils rather than those of other mediterranean-type ecosystems.