Spent mushroom substrate and cattle manure amendments enhance the transformation of garden waste into vermicomposts using the earthworm Eisenia fetida.

Garden wastes (GW) having high lignin contents could hinder the growth of earthworms and microorganisms in vermicomposting. This study investigated the Eisenia fetida-based vermicomposting of GW mixed with cattle manure (CM) and/or spent mushroom substrate (SMS) at different ratios of GW alone (control), 3:1 GW:SMS, 1:1 GW:SMS, 3:1 GW:CM, 1:1 GW:CM and 2:1:1 GW:SMS:CM to promote earthworm growth and improve the final vermicompost quality. In general, treatments with the addition of SMS and/or CM increased the survival rate, biomass, cocoon and juvenile numbers of E. fetida compared to the control. The addition of SMS and/or CM also significantly increased the activities of dehydrogenase, cellulase, urease, and alkaline phosphatase compared to the control. Furthermore, the addition of SMS and/or CM facilitated the decomposition of organic matter, cellulose and lignin, increased nutrient (N, P and K) concentrations, and accelerated nitrification compared to the control. The addition of SMS and CM led to greater chemical changes of the substrate compared to control. Heavy metal concentrations were increased in the final vermicomposts comparatively to the initial materials, but none of them exceeded the permissible limits. The highest germination index of Chinese cabbage and tomato seeds were both observed in the treatment of 2:1:1 GW:SMS:CM which reached 146.9 and 148.1. Overall, the 2:1:1 GW:SMS:CM treatment had the highest growth and reproduction rates of E. fetida, higher percentage degradation of organic matter, cellulose and lignin, as well as the best quality of the final vermicompost.