EFFECT OF VERMICOMPOST AND VERMICOMPOST EXTRACT ON OIL YIELD AND QUALITY OF PEPPERMINT (Mentha piperita L.)

Organic fertilizers have beneficial effects on plants growth and quality. However, vermicompost increases electrical conductivity in soil due to increased salinity associated with continued usage. The experiment was conducted in a research field at the University of Guilan to determine effects of 7 Mt ha-1 of cow manure vermicompost, vermiwash prepared from 7 Mt ha-1 of vermicompost, leachate vermicompost + vermiwash, 50 Mt ha-1 municipal solid waste compost (MSWC), chemical fertilizer (NPK 50–0–300) and no fertilization as a control on peppermint yield and quality. Fertilizer type affected all measured characteristics except number of nodes, stem fresh weight, total phenols and antioxidant capacity. Plants treated with vermicompost, vermiwash or leachate vermicompost + vermiwash were the tallest and had the highest levels of chlorophyll a, chlorophyll b, total chlorophyll and carotenoids. Plants treated with vermicompost or vermiwash had the highest total plant fresh weight, leaf fresh weight and total fresh yield. The leachate vermicompost, vermiwash and vermicompost can be used as organic fertilizers for sustainable peppermint cultivation.