Changes in the chemical and biological characteristics of grape marc vermicompost during a two-year production period

Abstract

In this study, the changes in the chemical and biological characteristics of a grape marc vermicompost during a two-year production period were studied to determine the time required for completion of the maturation phase and production of stable vermicompost. Grape marc was added to the surface of a vermireactor monthly for two years. At the end of the experiment, the resulting vermicompost was 100 cm deep and consisted of layers of fresh (top) to processed (bottom) grape marc approximately 15, 30, 180, 360, 540 and 720 days old. Several chemical and biological characteristics were measured in each vermicompost layer at the end of the experiment: the moisture content; pH; electrical conductivity; organic matter content; total and dissolved carbon content; C:N ratio; nutrient content; earthworm density; basal respiration; and the activity of 12 enzymes associated with the carbon, nitrogen, phosphorus and sulfur cycles. The earthworm density increased 30-fold during the two-year period. In addition, the pH and electrical conductivity as well as the organic matter, total carbon, dissolved organic nitrogen, phosphorus, potassium and copper contents all decreased, while the calcium, sulfur, zinc and manganese contents increased. Basal respiration and carboxylesterase, peroxidase and catalase activities were highest during the first 30 days. By contrast, the urease, acid phosphatase, alkaline phosphatase and arylsulfatase activities were greater after 30 days. The major changes in vermicompost occurred during the initial phase of vermicomposting. However, the chemical and biological characteristics continued to vary during the maturation phase because of microbial activity. Thus, the quality of vermicompost greatly depended on the duration of the maturation (conditioning) phase; therefore, it was difficult to determine the time required to yield a stable product.