Efecto de la siembra directa sobre los procesos de adsorción de fósforo en los molisoles del centro norte de la provincia de Córdoba (Argentina)

Under the hypothesis that the stratification of soil properties under directseeding conditions (SD) modifies P sorption parameters, the objectives of this work were: i) to estimate P sorption parameters by using Langmuir isotherms in samples of different depth, extracted from fields under continuous direct seeding; (ii) to analyze the similarities and differences between the parameters obtained; and (iii) to identify the relationship between the edaphic properties of the surface stratum and the estimated parameters. Soil samples of 0 to 5 and 0 to 20 cm were equilibrated with  solutions with increasing concentrations of P. From the relationship between the adsorbed P and the concentration of P in equilibrium, the maximum adsorption capacity (Qmax) and the retention affinity constant (k) were estimated. The higher Qmax and the low k of 0 to 5 cm samples show that there is a distinct behaviour in the first centimeters of depth. In that layer the bioavailability of P and the residuality of the applied fertilizers are regulated by adsorption phenomena responding to the  presence of organic colloids, which are accumulated by the stratification associated with SD.