Effects of land-use system and land-use change on soil enzymatic activities

Deforestation in the tropics has long been considered to lead to the degradation of the soil properties related to soil fertility. In addition, present agriculture in tropical countries is not sustainable due to decreasing soil fertility. The present situation of on-going land degradation in the tropics has not been well documented from the microbiological viewpoint. Soil enzymatic activity is an important biochemical parameter to evaluate the soil fertility because of the involvement of several soil enzymes in cycles of nutrients available to crops. We carried out studies on effects of land-use change on soil enzymatic activities (acid and alkaline phosphatases, P-glucosidase, arylsulfatase, and urease) in South Sumatra, Indonesia. We determined enzymatic activities under standard laboratory conditions to estimate the potential impact of land-use change and continuous cultivation of particular plants on soil fertility. Activities of soil enzymes were significantly higher in primary and secondary forests than in coffee plantations and cultivated lands in hilly areas. The activities of soil enzymes were closely related to the soil organic C and total N contents. In contrast, longer and repeated histories of deforestation and land-use change in middle terrace areas resulted in no consistent difference in soil chemical properties and soil enzymatic activities in relation to the land-use systems. Soil erosion is a process accelerating the soil degradation in the tropics. Plant cover (Paspalum conjugatum) on coffee plantation lands in hilly areas with steep slope resulted in significant decrease in soil erosion as well as the maintenance of high soil enzymatic activities.