There has been an upsurge of interest in organic fertiliser. Vermicomposting, or composting with earthworms, transforms organic substrates into a nutrient rich product through complex interactions between earthworms and microbes 1. Water from this process, vermicompost leachate, can be a nutrient rich fertiliser 2. Potential plant beneficial microbes exist in vermicompost 3 while microbes in leachate remain unexplored.
The aim of this project was to investigate leachate microbes from different starting substrates and examine changes with time. Banana, bean and melon, alone and in combination, were subject to vermicomposting. Molecular and culture techniques were used to analyse leachate microbial biodiversity. Leachates were stored for one year and analyses repeated to determine whether this product is the same microbiologically over two growing seasons.
Leachates from different substrates contained similar numbers of cultivable microbes. Refrigeration for one year saw a reduction in fungi and no change to bacteria. Storage at ambient temperature was more complex, with reduced bacteria from two food combinations and reduced fungi from one combination.
Leachates from different substrates contained different bacterial populations as determined by ARISA fingerprints. Storage of banana leachate at ambient temperature produced a population with the same fingerprint as fresh leachate. Refrigeration of leachate from three food combinations also resulted in the same fingerprint as the corresponding fresh leachate. Bean, melon and one food combination showed differences between fresh leachate and leachate stored at both temperatures.
This study shows that inputs into vermicompost play a role in the microbial population of the final product. The microbial population changes with vermicomposting time. Long-term storage can change the leachate microbes, changes which vary with storage temperature.