Abstract

This study assessed both the physico-chemical properties of winery solid waste (WSW) composts with or without microbial inoculation and the phyto-toxicity of their extract. Four different composts with initial pile height of 1 or 1.5 m were prepared through aerobic thermophilic process by mixing the filter materials (FM) and waste plant materials at 40: 60 ratio on dry volume basis. Cured composts were evaluated for selected physicochemical properties and germination attributes at varied extract concentrations (0, 10, 25, 50 and 100%) using cowpea, maize and tomato seeds. Microbial inoculation exerted significant effects on compost Bray-P2 content, while interaction between inoculation and compost pile size similarly had significant effect on ammonium-N content. The contents of bulk density, volatile solids, water holding capacity, pH, electrical conductivity, nitrate-N and exchangeable K among the various composts did not differ significantly. The composts possessed high electrical conductivity (range: 9.03–10.23 dS/m) suggesting high soluble salts concentrations. Compost type and extract concentration interaction exerted significant effect on the germination index (GI) of all three crops; with phyto-toxic effects on maize and tomato at 50% extract concentration and beyond. The compost extracts showed varying degree of phyto-toxicities to maize and tomato, while cowpea experienced no phyto-toxicity effect. Besides, the composts also showed phyto-nutrient and phyto-stimulant capabilities with greater than 100% root length and GI values. Nonetheless, the phyto-toxicity recorded in maize and tomato can be eliminated using lower application rates.