The role of local earthworms in plant nutrient addition in the Ethiopian Drylands

Abstract

The Ethiopian Drylands are rich in their variety of local earthworm species.However, the category of species, and the effect of their performance on additions to plant nutrients have not been adequately evaluated. Thus, local earthworm samples were collected from the three major agroecological zones (highland, midland, and lowland) in Tigray (northern Ethiopia) and classified down to species level. Moreover, a vermicomposting experiment with four treatments (three local earthworm species, Eisenia fetida, and a conventional composting method) and three replications was established. Finally, each bin's mature compost sample was taken to analyze plant nutrient content. The study results indicated that earthworm species in the highland, midland and lowland agroecological zones were Dendrobaena veneta, Eisenia andrie and Lumbricus rubellus, respectively. The use of these earthworms in the composting process (average of the four earthworm species) yielded higher nutrient content, ranging from 21.9 % for Sodium to 3300 % for Boron, compared to the conventional one. The highest total nitrogen (an increase of 44.4 %) and organic carbon (an increase of 33.4 %) were recorded in the Eisenia fetida and Dendrobaena veneta treated bins, respectively. Composting with Eisenia andrie has resulted in increases in P (96.1 %), K (125 %), Mg (83 %) and all micro-nutrients (between 91 % for Zn and 4400 % for B). Both Eisenia andrie and Lumbricus rubellus species contributed to the increased additions of Sulfur (85.7 %) compared to the control. It can be concluded that the use of local earthworms (particularly Eisenia andrie) in the composting process plays a significant role in plant nutrient addition.