A Microbiological Study of Earthworm Casts

SUMMARY Microbiological, physical and chemical changes were followed in worm casts ageing in the field. Filamentous fungi and yeasts increased in number rapidly after the cast was produced, but not bacteria or actinomycetes which were initially numerous. Measurements of hyphal length confirmed the increased growth of fungi. Ageing casts showed a declining respiratory activity, possibly because the bacteria formed resting stages. Aggregate stability increased rapidly as casts age, probably due to increasing amounts of fungal hyphae. Polysaccharide content of casts was much greater than that of soil, but did not vary with changes in stability. Total and mineral nitrogen levels of casts were greater than those of soil; the major part of the inorganic nitrogen occurred as ammonia which was rapidly converted to nitrate.