Grape pomace compost as a source of organic matter: Evolution of quality parameters to evaluate maturity and stability

The Pisco and wine industry in Chile generates about 400,000 tonnes/year of grape pomace as organic wastes (OWs). This material can be composted and used as organic fertilizer or amendment in grape orchards located in inceptisol soils with a very low organic matter as a strategy to increase soil and grape quality. The maturity and the stabilization of compost define the potential use of OWs as an amendment. Therefore, the objectives of the present study were focused to evaluate the evolution of chemical, microbiological, biochemical and phytotoxicity parameters during the composting process using grape marc and other components. The experimental study consisted of nine opened piles constituted by grape pomace, goat or horse manure. The piles were evaluated for 180 days in winter-spring seasons and mechanical turns were carried out every 10 days. The results indicated that humic to fulvic acids content ratio (Ha/Fa) could be used as process evolution indicator. The potential enzymatic activity of alkaline phosphatase and β-glucosidase, and microbiological functional groups like cellulolytic, amylolytic and phosphate solubilizing bacteria were strongly correlated with production of fulvic and humic acids (p ≤ 0.01). The compost derived from treatments complies with Chilean National Standard - NCh 2880/04, 2016 for the quality of organic amendments including low phytotoxicity with a radish germination %> 92% and absence of Salmonella sp., and fecal coliforms <1000 NMP/g. In conclusion, quality parameters evaluated showed sensitivity to evaluate both the composting process and compost quality.