Hydrolases Activities of Extracted Humic Substances During Vermicomposting of Damaged Tomatoes Wastes Using a Continuous-Supplying System

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Abstract

The behaviour of extracelullar hydrolytic enzyme activities in a continuous-supply vermicomposting system has never been studied previously. The aim of this study was to assess under such system the extracellular enzyme activities glucosidase, urease, acid phosphatase, and protease, which were extracted following the pyrophosphate-extraction method at pH 7.1. Vermicomposting was carried out using a medium-sized rectangular vermireactor continually supplied with damaged tomatoes (10 kg week−1) during a 5-month period on a layer of mature sheep manure. The earthworms were then removed, and the vermicomposted organic material was matured over a 2-month period. Total earthworm biomass reached its greatest value after 3 months, coinciding with peak levels for pyrophosphate-extractable carbon content and extracellular urease, acid phosphatase and protease activities. Extracellular β-glucosidase activity peaked in the 4th month, when microbial activity was also at its greatest level. At the end of the vermicomposting period, phosphatase and protease activity decreased to levels similar to those recorded at the beginning of the vermicomposting process. By contrast, β-glucosidase and urease activity values were grater than those recorded at the start of the vermicomposting process. Humic-enzyme complexes generated during the vermicomposting period were unable to resist denaturation, inactivation, and degradation caused by the air-drying during the maturation phase. Although the mature vermicompost obtained showed higher content in humus-enzyme complexes than the initial mature sheep manure, the assayed continuous-supply vermicomposting system was unefficient for enhancing the formation of stabilized humus-enzymes complexes.