Relationships between soil characteristics and productivity of Acacia mangium in South Sumatra

The variation in the morphological and physico-chemical properties of soils of Acacia mangium plantations were studied in South Sumatra, Indonesia in order to understand how these might affect plantation productivity. Representative soils consisting of four high productivity sites (HPS) and five low productivity sites (LPS) were selected. The main difference between the two productivity classes was in subsoil morphology. HPS soils had deep pisoplinthic horizons and were classified into Pisoplinthic Acrisols, LPS soils had shallow plinthic horizons and were classified into Acric Plinthosols. Differences in redox environments and water drainage in subsoil were the most likely factor creating the differences in morphology. Lower Fe-o/Fed values in HPS subsoil indicated that better drainage facilitated the dehydration and crystallization of iron oxides to convert plinthic into pisoplinthic. Productivity of Acacia plantations was correlated with subsoil characteristics. Subsoil of LPS with lower porosity and higher penetration resistance restricted deep root development, and consequently growth of Acacia, while that of HPS with higher porosity did not. The chemical characteristics of soils were also related to Acacia growth; subsoil of HPS had lower exchangeable Al, Al saturation, and higher soil pH; meanwhile T-C, T-N, T-P, available P and exchangeable cations of HPS and LPS were not significant different. Site classification based on subsoil characteristics, especially water drainage, and subsoil management to avoid soil compaction will be crucial for site selection and sustainable productivity of Acacia plantations.