Responses of earthworm abundance and production of surface casts and their physico-chemical properties to soil management in relation to those of an undisturbed area on a semi-arid tropical alfisol

Population densities of earthworms and their surface cast production were sampled across 15 soil management treatments such as annual tillages with organic amendments and perennial ley treatments during 1989-93 in a semi-acid tropical Alfisol. They showed significant reduction in their densities in annual treatments due to carbofuran and herbicide application during July 1989. In 1992, densities recovered from insecticide stress after 3 years, and showed significant temporal and spatial variation across the treatments, being higher during the post-rainy season. Soil management practices significantly affected the densities which were higher in zero-tillage farmyard manure treatment and in zero-tillage Stylosanthes and pigeonpea and Stylosanthes treatments among the annual and perennial treatments, respectively. Surface cast production of earthworms was higher in 1992 than in 1993, and was significantly affected by the annual treatments (P < 0.05). However, the physico-chemical properties such as pH, electrical conductivity (EC), organic C, total N, available P, available K, Na, Ca and Mg of casts were not affected by the annual and perennial treatments. The densities of earthworms, and their surface cast production were significantly greater in a natural revegetation area than those in the arable area under soil management, while most of the physico-chemical characteristics of casts were higher than those of the underlying soil in both arable and natural revegetation areas. (C) 1997 Elsevier Science Ltd.