Q.What are earthworm casts?

Vermiculture is the deliberate use of earthworms to convert organic food waste into vermicompost, a nutrient-rich material that sustains plant growth, with the goal of continually growing the worm population for a sustainable harvest. Earthworms used for this fall into two functional groups — surface-dwelling, darker-coloured humus formers (the group actually used for vermicomposting) and deeper-burrowing humus feeders that keep soil porous — and India's vermiculture units draw on both native species (Periyonyx excavatus, Lampito mauritii, Octochaetona serrata) and introduced exotic species (Eisenia fetida, Eudrilus eugeniae). A practical unit is built as a shaded, layered pit (gravel, then coarse sand, then a loading layer of soil or biomass) where the worms are introduced and left to process the waste, releasing visible castings on the surface that signal harvest time; a separate liquid by-product, vermiwash, is collected from the bed's drilospheres and used as a nutrient-rich foliar spray. Because earthworms sustain the bacteria, fungi a …