Influence of agricultural land use on the size and composition of earthworm communities in northern KwaZulu-Natal, South Africa

Abstract

The effects of land management including undisturbed native forest, native grassland, sugarcane ( Saccharum spp.) (preharvest burnt or green cane harvested), exotic forest (gum, Eucalyptus grandis; pine, Pinus elliottii; wattle, Acacia mearnsii), orchard crops (orange, Citrus sinensis; banana, Musa accumunata; avocado, Persea americana) and grazed kikuyu grass ( Pennisetum clandestinum) on the size and composition of earthworm communities and on related soil properties (organic C, soluble C, microbial biomass C) were investigated. The study locality was in the tropical, northern part of KwaZulu-Natal. Earthworm numbers followed the order: kikuyu pasture > native forest > banana> orange> wattle= pine= gum= green cane harvested sugarcane ≥ native grassland = avocado≥ burnt sugarcane . Earthworm numbers and biomass were closely positively correlated with soluble C, microbial biomass C and also pH. A total of 11 species of earthworms were collected. Over 80% of individuals collected were accidentally introduced exotic species which originated from India, South America and West Africa. Most land use types supported five to seven species but sugarcane and wattle supported only two or three species. Juveniles dominated the community under all land uses except kikuyu pasture and avocado. Epigeic species dominated under native forest and native grassland, avocado and gum. For the other types of land use, endogeics predominated. The most numerous species present was Pontoscolex corethrurus which was present under all land uses. The most common epigeic species was Amynthus rodericensis which made up a substantial portion of the community under native and gum forests and banana. The third most numerous species was A. minimus which is a polyhumic, endogeic species and was particularly numerous under kikuyu pasture. Dichogaster saliens was an important component of the community under some land uses. It was concluded that land use has major effects on the size, composition and diversity of earthworm communities in the region.