Evaluation of Proportions of Vermicompost and Coir in a Medium for Container-Grown Swiss Chard

Abstract

A mixture of vermicompost and coir is commonly used for growing plants. However, the extent to which variation in proportions of these substrates in a mixture affects plant growth is not known. A study was carried out in a greenhouse to determine appropriate proportions of vermicompost and coir mixture to produce the most suitable medium conditions for growing Swiss chard [Beta vulgaris L. ssp. cicla (L.) W.D.J. Koch]. Treatments were coir alone, commercial potting mix alone, and a vermicompost–coir mix in ratios of 2:1, 1:1, and 1:2. Electrical conductivity (EC), pH, water-holding capacity (WHC), and plant growth and nutrient content were improved when the proportion of vermicompost was increased from 0% to 67%. The ECs of vermicompost and coir alone were 2.80 and 0.50 mS·cm−1, respectively. After mixing, ECs were modified to 1.6, 2.1, and 2.5 mS·cm−1 for treatments with ratios of 1:2, 1:1, and 2:1, respectively. Plants in vermicompost had high amounts of N, P2O5 and K2O compared to plants in coir alone or the commercial potting mix. Addition of coir increased the WHC of the mix. The WHC of coir alone and the 1:2 mix were over 80%. Water loss by evaporation was lowest in the 2:1 mix; evapotranspiration was highest due to active plant growth, which led to greater leaf expansion, increased leaf number, and harvest weight. Plants grown in coir alone had the highest percentage of dry matter. A ratio of 2:1 vermicompost–coir mix is recommended for container-grown Swiss chard greens.