PHOSPHATE DISTRIBUTION IN SOILS OF THE CENTRAL ARGENTINEAN PAMPA

Phosphate is in the Argentinian Pampa a plant nutrient, which limits growth in relation to the geomorphic position of the sites. The pattern of potential P-uptake by plants is determined by total P amount and it's availability. Even in the almost flat land, total and available P in soils differ in and around depressions. Eroded soil material impoverishes the slopes and enriches the depressions with P. Loose slope soils are rich in lime and therefore act as a strong P-sorbent. Although the depression have high active Fe-oxide contents, at a neutral to slightly alcaline pH the P-availability is still sufficient. The amount of organic matter is in the semiarid region the main factor controlling P-uptake and therefore soil fertility. P-fertilisation will be most effective on plain soils, because on slopes low availability and fixation and in depression sufficient supply of P are expected.