The effects of Eucalyptus sp. plantations on Uruguay natural resources.

Part II: soils

Abstract

Knowledge about Eucalyptus Sp. plantations on Uruguayan soils, generated in research projects by the Soils and Water Dept. of the Fac. of Agronomy-UDELAR is synthesized. Based on 12 cases studied, forested soils presented lower pH, higher exchangeable aluminium, and lower base saturation than soils under the previous grassland. Based on seven cases studied, soil organic carbon tended to decrease in the upper A horizon. Although there was no clear result for other horizons, in some cases organic carbon tended to increase in the lower A or the upper B under trees, compared with the soil under grasses. Even though this changes in vertical distribution could determine no change in the total carbon content of the profile; the presence of the O horizon on the forested soils would allow to conclude that the plantations increase total organic carbon in the soil. Five years of soil water content monitoring in the same soil under forest and under the previous grassland, showed lower values under trees all the time. During summer this was due to higher evapotranspiration under trees and during winter it was due to lower soil water holding capacity of soils under eucalyptus. Soil degradation by former land use showed negative impact on productivity in two experiments. If good control of previous vegetation and weeds is achieved using herbicides, based on 4 experiments, it is concluded that tillage is not needed in eucalyptus plantations, independently of previous soil use.