Changes in biochemical properties of cow manure during processing by earthworms (Eisenia andrei, Bouche) and the effects on seedling growth

The biochemical changes in fresh cow manure caused by the earthworm Eisenia andrei (Bouche) were measured over a period of four months, under controlled laboratory conditions. Earthworms were introduced into each of four plastic containers (0.4 x 0.27 x 0.15 m) containing fresh cow manure (2500 g), and four containers containing manure but without earthworms served as controls. Earthworms reduced the pH and decreased the moisture content in the manure. The C:N ratio of the manure with or without earthworms decreased progressively from 36 to 21. The ash and total nitrogen contents increased greatly for a few weeks after the introduction of earthworms, reflecting a rapid breakdown of carbon compounds and mineralization of nitrogen by the earthworms. CO2 evolution decreased rapidly (44 %) one week after the introduction of earthworms, and continued at a lower rate throughout the 17 weeks (51 % reduction as compared to 22 % without earthworms), indicating increasing stability of the organic matter. Earthworms reduced microbial biomass early in the process, but enhanced nitrogen mineralization and increased the rates of conversion of ammonium-nitrogen into nitrate. The major general effect of earthworms on the organic wastes was to accelerate the maturation of the organic wastes as demonstrated by enhanced growth of lettuce and tomato seedlings.