Slash and burn agriculture at higher elevations in north-eastern India. II. Soil fertility changes

The effect of ‘slash and burn’ agriculture (jhum) on soil fertility at higher elevations of Meghalaya, north-eastern India was investigated, comparing and contrasting 15, 10 and 5-year jhum cycles. The pH of the surface soil increased after the burn and gradually decreased during cropping and subsequent fallow development. Nutrients such as carbon and nitrogen are volatilized by the burn and declined, at least in the initial phase of cropping. However, nitrogen recovery started during the later phase of cropping. Available phosphorus followed a more or less similar pattern as nitrogen. On the other hand, cations increased markedly after the burn and were depleted during cropping. In general, the nutrient level under a 5-year jhum cycle was significantly lower than under 10 and 15-year cycles. The recovery pattern during fallow development had an initial phase of depletion, up to about 5 years, followed by recovery. This suggests that a jhum cycle of 5 years, now prevalent in the region, is definitely too short. The generally lower nutrient status under a terrace system after cropping, even when compared to a 5-year jhum cycle, suggests that a terrace system could not be sustained without a heavy input of fertilizers.