DIFFUSION OF ANIONS IN A TYPIC HAPLUSTOLL. EFFECT OF SOIL USE

Abstract

Ion exchange and the dissemination of agrochemicals or pollutants depend, to different extents, on the diffusion of the chemical species involved. Modeling the transport and dis-persion of different substances in the soil requires the knowledge of the parameters that determine their rate of diffusion in the soil environment. The objective of this work was to determine the diffusion coefficients of phosphate and chloride anions in a Typic Haplustoll of the central region of the Province of Córdoba, Argentina, affected by different intensity of cultivation. The situations evaluated were: 1) no cultivation, (in a closed area), 2) alfalfa meadow rotating with other pastures in the last 50 years and, 3) a continuous agriculture plot, with more than 80 years of continuous agriculture (initially peanut/currently soybean). The diffusion experiments were carried out in saturated soil columns, generating flow from a soil column fertilized with the ion of interest, towards a soil column with its natural level of these ions. The diffusional transport parameter showed a high sensitivity to the soil history of use, constituting an indicator of its physical and chemical quality as a support for plant growth. The phosphate diffusion coefficient (D), in the conditions of this study, was mainly related to the bioavailability of the nutrient, defined by the concentration in the solution, which unfolds the position of the matrix/solution equilibrium towards the solid phase. The estimated average D values, for phosphates, differ significantly between the situations evaluated, decreasing as the intensity of agricultural activity increases. In the case of chlorides, no significant differrences were observed between treatments.