Nutrient Dynamics in Eucalyptus Plantations of Different Ages before and during Intercropping

Abstract

The study characterized and monitored changes in soil nutrients under different ages (1.5, 3, 6, 12, 20 and 40 years) of Eucalyptus grandis tree plantations and its tissues (litter and fresh leaves) before and during intercropping. Soil sampling for characterizing tree plantations was at; 0-20 cm, 20-40 cm, 40-60 cm, 60-80 cm, 80-100 cm depths while for monitoring nutrient changes during cropping was at 0-20 cm, 20-40 cm depths in crop plots. The planted crops under the trees were Irish potatoes where no fertilizer was applied. Radial cluster sampling in RCBD was used in plantations. Litter and fresh leaves were sampled from trees of ages 1.5, 3, 6, 12, 20 and 40 years. From the results; Eucalyptus tree age significantly affected nutrient concentrations in the understory soils i.e. available phosphorus, pH, calcium, potassium, magnesium and iron. In addition, the age of Eucalyptus influenced the concentrations of nutrients in canopy litter and its leaves i.e. total nitrogen, total phosphorus, total calcium, total potassium, total manganese and total iron. Potassium, magnesium, manganese and organic carbon levels were high in soil, litter and leaves. Crop cultivation under Eucalyptus trees reduced total nitrogen, potassium and calcium in the soil while available phosphorus, pH, magnesium and manganese increased. Soil carbon was unchanged. From this study, soil nutrient dynamics under Eucalyptus trees permits successful crop growing especially with the correct species of crop and tree spacing. However, phosphorus deficiency and possibility of manganese toxicity were the possible limitations to successful crop production under the trees.