The decomposition and upgrading of agricultural wastes by the earthworm Eisenia fetida (Savigny 1826).

Abstract

Cattle slurry from various sources, both digested and undigested, was tested as a culture medium for growing the earthworm Eisenia fetida. Earthworm growth was related to the physical-chemical characteristics of the slurry and the presence of bulk organic material. Cattle slurry from several sites which had been mechanically separated to produce a stackable solid had different physico-chemical characteristics and produced varying earthworm growth responses. In particular, solids from Bore Place farm had a high ionic conductivity and ammonium ion concentration which reduced growth. The woodchip bedding used was found to be inhibitive to E.fetida. Solids that were pretreated by high temperature composting as opposed to room-temperature aging before earthworm inoculation generally produced a higher earthworm biomass, but only after an initial inhibitory effect was overcome. The residue of anaerobically digested cattle slurry can also be used to support E.fetida, although in some cases the digestion process can inhibit subsequent earthworm growth. The addition of cellulose to cattle waste, using different cellulosic bulking agents, showed the importance of both the form of carbon present and the C/N ratio on earthworm growth, effecting both nutritional and environmental qualities of a waste. Results using an artificial cellulose based medium showed how earthworms require a complex waste ecosystem in equilibrium to survive. Under laboratory conditions E.fetida does not provide a major contribution to the changes in physico-chemical characteristics during decomposition of cattle solids compared to the action of micro-organisms. The main effect of earthworms may therefore be purely physical in nature, macerating the solids and reducing particle size. Undigested and digested worm worked material can support plant growth but requires further pre-treatment such as bulking with peat to allow plant growth equivalent to a commercial compost.