A Microbiological Study of Earthworm Casts

Abstract

SUMMARYMicrobiological, 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.

Space-time dynamics in situ of earthworm casts under temperate cultivated soils

“…On the contrary, a calm-period of weather without much rainfall is favorable for the stabilization of earthworms casts during the ®rst few days. The stabilizing process within casts could be related to (i) the decrease of the cast water content that led to the increased linkages between soil particles (Molope et al, 1985;Marinissen and Dexter, 1990) and (ii) the colonization of casts by fungi (Parle, 1963;Tisdall and Oades, 1982) or by moss as we observed in this study. Both stabilizing phenomena might have been at the origin of the critical 10-d old threshold, that we outlined, below which casts disappeared quickly and beyond which cast disappearance slowed down.…”

Quantifying the Effects of Earthworms on Soil Aggregation and Porosity

“…Prior to the mid-1980s, most studies suggested that freshly excreted earthworm casts were immediately more stable than uningested soil (Hopp and Hopkins 1946;Dutt 1948;Swaby 1950;Teotia et al 1950;Parle 1963;Lal and DeVleeschauwer 1982;Lal and Akinremi 1983). These results, however, were mainly attributable to the fact that the samples were dried before analysis.…”

Exotic Earthworm Invasion and Microbial Biomass in Temperate Forest Soils

“…Several studies have shown that earthworms reduce microbial biomass, primarily by consumption, as soil passes through the earthworm gut (Wolters and Joergenson 1992;Bohlen and Edwards 1995;Devliegher and Verstraete 1995;Zhang and Hendrix 1995;Gorres and others 1997;Callaham and Hendrix 1998;Saetre 1998;Zhang and others 2000;Lachnicht and Hendrix 2001). In contrast, other studies have found earthworm-induced increases in microbial biomass (Parle 1963;Shaw and Pawluk 1986;Daniel and Anderson 1992;Scholle and others 1992;Tiwari and Mishra 1993;Burtelow and others 1998;Bohlen and others 1999). Devliegher and Verstraete (1995) suggest that the net effect of earthworms on microbial biomass is a product of reductions in biomass during gut passage and stimulation due to mixing of organic matter into the soil profile.…”