Comparison of the effects of compost and vermicompost soil amendments in organic production of four herb species

The aim of this study was to compare the effects of using compost and vermicompost as soil amendments in organic herb production, using four herb species (Dracocephalum moldavica L., Melissa officinalis L., Nepeta cataria L. and Thymus vulgaris L.) as model plants. Plants were cultivated in a greenhouse in containers filled with soil from an organically certified field and that had been amended with equal rates of cow manure compost or vermicompost [0%, 10%, 20% and 30% (v/v) for M. officinalis and N. cataria, and 0%, 20%, 30%, and 40% (v/v) for D. moldavica and T. vulgaris]. The four herbs showed different sensitivity to the incorporation of the organic amendments, with the optimum rate differing between the species: 20% was shown to be optimum for both amendments in the case of M. officinalis and N. cataria, and 20% for compost and 30% for vermicompost in the case of D. moldavica and T. vulgaris. However, at identical amendment rates, the vermicompost treatment resulted in higher plant biomass compared with the compost. The organic amendments tended to increase the concentration of K⁺ in the leaf tissue in all species. The NO₃^– concentration in the leaf tissue tended to increase with increased rates of the organic amendments, but both amendment-specific and species-specific effects were evident. It was concluded that the use of vermicompost was superior to that of compost for organic herb production in containers.