Chemical and Microbial Characteristics of Vermicompost Leachate and their Effect on Plant Growth

Abstract

There is interest in reducing chemical fertiliser in favour of organic amendments. Vermicompost leachate is the liquid resulting from organic waste breakdown by earthworms. Little is known about effects of different organic substrates on leachate properties. Various substrates were tested for their effect on earthworms, leachate chemical and microbial composition, and benefits to plants. Effect of 18 substrates on earthworm population and mass was measured over 8 weeks. Earthworm growth and survival varied with substrate. T-RFLP analysis from 6 substrates at 4 and 8 weeks showed differences in leachate bacteria and fungi. Banana(B), green bean(G) and rockmelon(R) were used, alone and in mixes. Earthworm population, mass, life cycle stage and cocoon number were measured over 16 weeks. ARISA analysis at 10 weeks showed differences in leachate bacteria. Leachates were stored for a year at 4°C and 24°C. Most leachate chemical and microbial properties changed with storage. Leachates from substrate mixes B/R or G/R were unchanged at 4°C. Leachates were applied to soybean, serradella and wheat. Unsterile G leachate increased soybean nodulation at 8 weeks and serradella nodulation at 10 weeks, but not at 5. Plant mass increased in chemically fertilised wheat at 5 and 10 weeks, and 5 for serradella. At 10 weeks there was no difference in serradella mass. G leachate effect on nodulation was tested on serradella. G leachate was compared with substrate mix of B/G/R leachate, synthetic G leachate, and chemicals (CRS). Microbes extracted from G leachate were applied. CRS produced the highest plant height and dry weight. Inoculation with G leachate microbes increased nodule mass in plants treated with CRS. Vermicompost recycles organic waste into a product that improves legume nodulation through microbial action and may increase biologically fixed nitrogen.