Vegetation, soil hydrophysical properties, and grazing relationships in saline-sodic soils of Central Argentina

Land use and grazing regime can influence the dynamic of soil water and sal t in humid areas. In Central Argentina, more than 2 x 10(6) ha are subjecte d to either permanent or cyclical processes of land salinization, alkaliniz ation, flooding and sedimentation. In this region, the natural vegetation i s the principal resource on which most systems of animal production are bas ed. The objective of this study was to evaluate the effects of plant cover and grazing over some hydrophysical properties of three saline-sodic soils (two Gleic Solonetz in duripan phase and one Mollic Solonetz in fragipan ph ase), within a catena sequence. The effects on bulk density, saturated hydr aulic conductivity, infiltration runoff, superficial salt accumulation and soil salinity distribution were determined in both bare and covered soil co nditions, inside and outside of grazing exclosures. The results showed incr eased bulk density of topsoil for bare conditions, while saturated hydrauli c conductivity did not show significant differences. In soils without any c over, the infiltration decreased significantly. Consequently, the runoff co efficient and salinity were greater, as indicated by significant salt accum ulation in the topsoil. The soil profile salinity was reduced as a function of exclosure time, showing a trend toward desalinization resulting from a combined effect of soil cover and changes in intensity of land use. A conce ptual model of salt and water dynamics in the soil profile for the landscap e scale is postulated. The role of vegetation in regulating water and salt movement in poorly drained areas is emphasised as a basis for the developme nt of management strategies.