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Composts and vermicomposts from a municipal composting plant in northwestern Patagonia, both having undergone a thermophilic phase, (with the vermicompost being inoculated with earthworms after the thermophilic stage) and a nonthermophilic backyard vermicompost were studied. Their effects on soil biological and biochemical properties and plant growth were evaluated in laboratory incubations and a greenhouse trial, using a degraded volcanic soil amended at rates of 20 and 40 g kg^sup -1^ of vermicompost or compost. Between the two municipal products, the vermicompost had significantly larger nutrient concentrations than the compost; when mixed with the soil, the vermicompost also had higher microbial populations size and activity, and produced increased ryegrass yields. Compared to the municipal compost, the backyard vermicompost had similar or higher nutrient concentrations but its effects on soil microbial biomass, soil microbial activity and ryegrass yields were lower. Our results suggest that no generalization can be made regarding the higher quality of vermicomposts vs. composts, because the product quality depends both on the original materials and the technology employed.
Introduction
The use of the organic fraction of municipal solid waste for agricultural purposes is becoming an established practice worldwide, because it reduces the volume of landfilled waste and provides a valuable agronomic resource (Zucconi and de Bertoldi 1987; He et al. 1995; Schultz and Roemheld 1997; Cooperband 2000).
Composting and vermicomposting are both recommended widely as biological processes for transforming organic wastes into useful soil amendments (Dominguez et al. 1997). Although both are biooxidative processes that stabilize organic matter, there are important differences between them. Composting includes a thermophilic phase (45 to 65°C), during which labile organic matter degradation occurs and pathogens are effectively reduced (Zucconi and de Bertoldi 1987; Golueke 1991). Vermicomposting does not involve a thermophilic phase (temperatures above 350C kill earthworms) and the coupled activities of earthworms and microorganisms stabilize the organic matter (Riggle and Holmes 1994; Dominguez et al. 1997). Furthermore, vermicomposting requires a moisture content of 70 to 90 percent (Edwards 1995), much higher than that required by composting, 40 to 60 percent (Golueke 1991). Because vermicomposting lacks a thermophilic phase, human pathogen reduction in the final product is not guaranteed. There is some evidence that vermicomposting effectively reduces human pathogens (Eastman et al. 2001), but it is not...