Phosphorous sorption process evaluated by soil and plant parameters

Abstract

The P sorption processes in soils were evaluated in 21 uruguayan soil samples (0-15 cm) developed from different parent materials. P adsorption isotherms were adjusted and different p Sorption indexes were calculated. Wide variation in P sorption was found among soils, associated to their iron oxides, clay and exchangeable aluminum content. Soils developed from igneous and basaltic rocks and some clayed sediments (Sedimentos Pelíticos Grises) showed the highest P sorption degree, whereas soils developed from sandy triasic and cretacic sediments showed low P sorption. High correlation between the differents sorption indexes were found. A glasshouse experiment was developed on the soils with differents levels of P added (0, 26.2, 52.4 and 78.6 mg P pot^-1), and P uptake in two cuts of ryegrass plants was evaluated. Low rates of P uptake by plants and low recovery of P added were found in soils with high P retention capacity. These results suggest lower efficiency of fertilizer addition for these soils. The different P sorption indexes were highly correlated with the differents rates of P uptake by plants.