Grape Marc and Beyond: A Critical Review of Decoding Vermicompost Applications in Viticulture - Impacts on Soil, Microbiota, Plant Nutrition, and Dark Aspects

Vermicompost is increasingly promoted as a circular, low-impact amendment for vineyard soils. However, its agronomic performance and constraints remain contrasting in several studies. This review integrates evidence on vermicompost produced from winery by-products (e.g., grape marc) and from non-winery feedstocks, both applied in vineyard systems. This review is organized around two complementary themes that remain underexplored in the literature, designed to capture the full vineyard ecosystem. (1) Effects of winery waste-derived vermicompost on crops and vineyards. We synthesize evidence on vermicompost produced from winery residues (e.g., grape marc), examining three outcome domains: germination and early growth, soils and microbiota, and yield and quality, first in Vitis vinifera L. and then in other crops. This cross-crop lens is used to identify shared mechanisms, dose ranges, and boundary conditions relevant to vineyard practice. (2) Application of vermicompost from alternative substrates in vineyard systems. We evaluate vermicomposts sourced from non-winery feedstocks (e.g., livestock manures) applied to vineyards, using the same three outcome domains. This tests the generalizability of benefits and risks beyond winery residues, enabling feedstock-specific comparisons (chemistry, maturity, salinity, micronutrients/trace metals). A whole-system vineyard perspective was adopted: circular flow of biomass from pruning residues and grape marc through their conversion into vermicompost, to its reintegration as an amendment in vineyards and, where relevant, in non-vine crops, thereby closing the grapevine-by-product loop. Finally, the last section addresses challenges and limitations (e.g., product heterogeneity, short study horizons, cation imbalances, metal mobilization, and methodological limits of microbiome inference), followed by Environmental footprint and Life Cycle Assessment considerations.