Soil amelioration by Acacia hybrid: An assessment of soil condition for re-establishing native species in the tropics

Tropical acacias are used for reforestation and recovery of degraded lands. This study aimed to evaluate the potential of Acacia hybrid (A. mangium x A. auriculiformis) to improve the physical and chemical properties of degraded soils. The experiment was carried out in second- or later-rotation Acacia hybrid plantations in Central Vietnam. A total of 109 soil samples was collected from the 0 – 20 cm topsoil of 30 plantations representative of five ages (0.5, 1.5, 2.5, 3.5 and 4.5-5.5 year-old) in six locations, and in nearby fallow land at each location. Acacia plantations significantly enhanced (P<0.05) total organic carbon (TOC), total nitrogen (TN), exchangeable calcium (Ex-Ca), magnesium (Ex-Mg), sodium (Ex-Na), electronic conductivity (EC) and bulk density (BD) when compared to fallow land. However, Acacia plantations increased soil acidity. Within the 5.5-year-old rotations examined, most soil properties were not significantly changed with increasing plantation age (P>0.05). However, the trends showed many nutrient properties declined during the first 2 or 3 years after establishment. After 4 years, TOC recovered to initial levels, though base cations remained lower. Soil properties were strongly related to initial soil and site factors such as clay content, gravel volume, slope angle and elevation.