Soil factors influencing yields of Eucalyptus camaldulensis on former tin-mining land in the Jos Plateau region,Nigeria

Plantations of Eucalyptus growing on reclaimed tin-minning spoil were compared with similar stands established on undisturbed farmland soils in the north of the Jos Plateau, Nigeria. Soils were collected from sample plots in both situations to determine their physical and chemical properties, while destructive harvests of representative stems were used to calculate tree yields.A principal components analysis of the soils data revealed wide variations in texture and base status, and was supported by a cluster analysis from which five major soil groups were defined. One such group, which contained a majority of mining site plots, was characterised by shortages of organic matter and low levels of available phosphorus. Farmland plantation sites had a wider range of texture and fertility, but on the whole gave similar yields to those of mining sites.The relationship between forest yield and selected soil variables was investigated using multiple regression analysis. This showed that the best yields occurred on fine-textured soils with good reserves of organic matter, while moderately base-saturated soils and high available-iron concentrations were associated with poor growth. There were indications that soil chemistry was modified by tree growth, with high-yielding stands increasing cation exchange capacity but significantly lowering soil pH.The implications for future tree growth are discussed, and suggestions given for the improvement of currently derelict mining sites.