Soil Fertility Under Homegarden Trees and Native Moist Evergreen Forest in South Andaman, India

This study describes variations in organic C; total N and P; mineral N and P; and exchangeable K, Ca, and Mg; and microbial biomass C in soils in relation to leaf litter and root biomass in three depths (0 to 10, 10 to 20, and 20 to 30 cm) at two canopy positions (under canopy and between canopy) of three 20-year-old homegarden trees: coconut palm (Cocos nucifera L.), clove (Eugenia cariophyllata Thunb), and nutmeg (Myristica fragrans Houtt. Nees) spice trees in South Andaman island of India. Control soils were sampled from an adjacent open plot. Concentrations of the nutrients under the trees were compared with that found in the native evergreen forest to evaluate several components of the sustainability of the homegarden agroecosystem. Organic C, total N, total P, exchangeable NH4+, NO3-, exchangeable K, Ca, and Mg were higher in the under canopy and between canopy positions of all the homegarden trees than that in the open plot. In addition, these values were higher under the spice trees than that under the coconut palm. All the elements, except Ca and Mg, were highest in the surface soil (0 to 10 cm) and decreased with the depth in all the treatments. Microbial biomass C was inversely related to the depth, and was the highest (454 g g-1) under coconut and the lowest (306 g g-1) under clove. Litter production was higher under the palm than under the spice trees, but concentrations of elements in the litter biomass were higher in the latter. Concentrations of nutrients (N, P, K, Ca, and Mg) in the forest litter and roots were well within the range found in the litter and roots of the homegarden trees. These seem to be reasons why homegardens in the islands are sustainable.