PHOSPHORUS ADSORPTION AND ITS RELATION TO SOIL PARAMETERS IN A CLIMOTOPOSEQUENCE OF THE SEMIARID PAMPAS IN CENTRAL ARGENTINA

Phosphate-sorption and - buffering capacity was studied in 15 A-horizo ns of mainly entic Haplustolls, developed parent materials with high c ontents of volcanic ash, situated along a climotoposequence of the Sem iarid Argentinian Pampas. The maximum sorption capacity (Xm) of the La ngmuir equation and the buffering capacity, represented by the product of a and b constants of the Freundlich equation, were analized and re lated to soil parameters. It was found that the highest values of <<a, b>> correspond to depression soils in the dryest area of the climosequ ence, with high organic matter-, exchangeable Ca- (Cai) and inorganic Fe (Fee, Fees, Feo-Fep) levels. Highest Xm values were found in soils on SW-slopes with the highest Cai and inorganic Al (Ale, Alos, Alo-Alp ) levels. Simple linear and multiple regression analysis showed that X m depends mainly on amorphous Al (Ale) and to a lesser extent on Cai, while buffering capacity shows a positive correlation with OM- and to a lesser extent with Alos- and inorganic Fe-contents.