Effects of Eucalyptus plantations on the physical and chemical properties of soil in floodplains of the eastern region of Paraguay

Resumo

The floodplains of the eastern region of Paraguay have soils with a shallow water table that causes flooding in months of heavy rainfall (August to December). The soils, predominantly Ultisols with gleyic properties, display high contents of soil organic matter (SOM) and an acidic pH. These environments are being transformed into Eucalyptus camaldulensis Dehnh. plantations, primarily for energy purposes. The aim of this study was to evaluate the chemical and physical properties of soils in eucalyptus plantations established on the native lowland grasslands. For this purpose, three chronosequences were selected, consisting of native grasslands and eucalyptus plantations aged between 2 and 8 years. In each system, the chemical and physical properties were determined at depth increments (0–5, 5–10, 10–20, and 20–40 cm). Each soil sample in the plots included six repetitions for both chemical and physical analyses. In the first years of eucalyptus planting, soil organic carbon (SOC) decreased by 50 %due to the intensive tillage carried out in the first years to establish the eucalyptus plantations. SOC concentrations recovered over time, although they did not reach the levels observed in the native grasslands. Soils with eucalyptus plantations displayed a higher bulk density (up to 1.35 g cm-3), greater acidity (pH value of 4), and a decrease in phosphorous (P) and exchangeable bases (up to 30 %) in comparison with natural grasslands. It is concluded that, in order to prevent the degradation of the chemical and physical properties of the soil in natural grasslands, it is necessary to plan practices that include land-use changes with native forest species and reconsider the practice of transforming these natural systems.