Effect of agricultural land use on soil organic matter status and the composition of earthworm communities in KwaZulu-Natal, South Africa

Abstract

Little is known regarding the effects of land use on soil organic matter status and earthworm communities in South African soils. For that reason the effects of the main agricultural land uses in the midlands region of KwaZulu-Natal (maize ( Zea mays), sugarcane ( Saccharum spp.), annual ryegrass ( Lolium multiflorum), permanent kikuyu pasture ( Pennisetum clandestinum), gum ( Eucalyptus grandis) and pine forest ( Pinus patula)) on soil organic matter content, microbial biomass C and the size and composition of the earthworm community was investigated on two sites where the long-term history of land management was known. In comparison with, undisturbed, native grassland, permanent kikuyu pasture resulted in an increase in organic C, K 2SO 4-extractable C, microbial biomass C and the microbial quotient. Maize and sugar production under conventional tillage (CT) resulted in a decrease in organic matter and microbial biomass. Under gum and pine forests the organic C content was similar to that of under native grassland but the microbial biomass and microbial quotient tended to be higher. Exotic earthworms dominated under agricultural management making up to 98 and 100% of the communities at sites 1 and 2, respectively. They belonged to the families Lumbricidae, Acanthrodilidae and Megascolicidae. They were accidentally introduced from Europe, India and West Africa, respectively, and now coexist in the sub-humid warm climate of the region. Earthworm numbers (230–310 m −2) and biomass, the number of species present, and the number present as adults were all greatest under kikuyu pastures and numbers were low (<60 m −2) under maize (CT) and sugarcane. Numbers were 3.5-fold higher for maize under zero than CT. In relation to the comparatively large organic C and microbial biomass C values under exotic forests, earthworm numbers were notably low (25–60 m −2). This was attributed to the low palatability of pine and gum litter. It was concluded that land use has substantial effects on soil organic matter content and on the size, composition and diversity of earthworm communities in South African soils.