Role of earthworms in nitrogen cycling during the cropping phase of shifting agriculture (Jhum) in north-east India

Abstract

We investigated the role of earthworms in the N cycle in a shifting agriculture system under a 5- and a 15-year Jhum system fallow period intervening between two croppings on the same site. Earthworms participated in the N cycle through worm cast egestion, mucus production, and dead tissue decomposition. Soil N was initially depleted by volatilization during slash and burn operations, and subsequently during cultivation processes. These losses were more pronounced under the 15-year Jhum system. We also studied the addition of N to the system in crop residues, through weed recycling, or in compost applied as organic manure under both the 5- and the 15-year Jhum systems. The total soil N made available for uptake by the plant through the activity of earthworms in this agro-ecosystem was higher than the total input of N to the soil through the addition of slashed vegetation, inorganic and organic manure, and recycled crop residue and weeds. Therefore, in highly leached soils of the humid tropics, worm activity is particularly, important because of rapid incorporation of litter into the mineral soils and because of local concentrations of nutrients in the surface soil layers.