Characterization of P adsorption properties of some agricultural volcanic soils from Canary Islands Spain 254

Phosphate sorption properties were evaluated for 28 agricultural soils from Tenerife, Spain. Of these, 16 were classified as Andisols and 12 as Alfisols. Phosphate sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine P sorption maximum of the soils. The two groups of soils differed considerably in their capacity to sorb added P. Andisols, on average, presented higher values of P sorption maximum, standard P requirement and P buffer power, and lower values of equilibrium P concentration than the Alfisols. When related to soil properties, P sorption maximum was significantly correlated with oxalate-extractable aluminum oxide and organic matter (P < 0.05) in the Andisols, and with oxalate-extractable aluminum oxide, clay, and organic matter content (P < 0.01) in the Alfisols. Simple measurements of the P sorption index (a single-point isotherm) were shown to reasonably estimate P sorption capacities of the soils.