Run-off and infiltration losses related to shifting agriculture (jhum) in Northeastern India

Abstract

Subsequent to slash-and-burn of the forested fallow, and during shifting agriculture (Jhum) in the northeastern hill areas of India, the system loses much of its capacity to hold soil nutrients. Various losses occur through wind-blow of ash and also through runoff and percolating water. The chemistry of the ash, and the amounts of run-off and percolating water, are related to the length of the Jhum cycle owing to the type of vegetation that is slashed and burnt. The runoff and percolation losses of water and sediment during cropping, increased with shortening of the Jhum cycle. As percolation losses are fairly high due to the generally porous soil, terracing of the land in the manner suggested by some as an alternative to Jhum is not considered ecologically sound. Drastic reduction of fertility through losses of sediment and nutrients occurred in both 5- and 10-years' fallows. The shortening of the Jhum cycle to 4-5 years does not permit the recovery of soil fertility and has adversely affected the vegetational cover and the biogeochemical and hydrological cycles.