Earthworm populations in a savanna-agroforestry system of Venezuelan Amazonia

Abstract

In the forest-savanna ecotone around Puerto Ayacucho, Amazonas State, Venezuela, characterized by sandy entisols and ultisols with very low natural fertility, some producers have established agroforestry systems (AFS) of production on savanna soils by adding animal manure as the main fertilizer. This paper examines the earthworm communities in a natural savanna (NS) and in an AFS supplied with organic fertilizers established over 25 years ago. Organic matter management of the savanna soils has strongly modified the earthworm populations in the studied AFS as compared with the original savanna soil. Earthworm density was found to be 1.6–4.8 times higher in the AFS than in the original savanna. The correlations among earthworm populations and soil parameters suggested that earthworms in AFS can be limited by the amounts of food (organic matter) present in the soil. Moisture, in turn, affects other parameters that are important for earthworm distribution. Our results emphasized the importance of appropriate organic-matter management and the relevance of earthworms in such agroecosystems. By promoting the use of the earthworm population as an agroecological factor linked to low levels of organic fertilization, it is possible to promote major agroecological sustainability in sandy savanna soils.