INFLUENCE OF DRYING AND AGING ON THE STABILIZATION OF EARTHWORM (LUMBRICIDAE) CASTS

The influence of drying and ageing on the stabilization of casts produ ced by the endogeic earthworm, Aporrectodea rosea, from a soil, which was hard-setting and low in organic matter, were investigated in the l aboratory. Casts and uningested soil were aged-most for up to 32 days, dried for up to 21 days, or subjected to different wetting and drying cycles over 30 days. The dispersion index of aged-moist casts decreas ed from 0.40 to 0.25 over 32 days, while dispersion index of dried cas ts decreased from 0.40 to 0.01 over 21 days. The dispersion index of a ir-dried casts was not significantly increased by five cycles of wetti ng and drying. The dispersion index of dried casts was not significant ly less than that of dried soil, In soils wetter than a matric potenti al of approximately - 35 kPa, stabilization of casts was probably due to a combination of cohesion of soil particles, age-hardening and grow th of microorganisms. However, in soils drier - than 35 kPa, cementati on was probably the major mechanism of stabilization. The addition of wheat straw to the soil prior to ingestion by earthworms increased dis persion from aged-moist casts, but did not influence dispersion from d ried casts. The addition of wheat straw decreased the number of air-dr ied casts which slaked severely. The concentration of soluble carbohyd rate decreased with dispersion index as casts and uningested soil were each dried. This suggested that soluble carbohydrate may have been de natured with or without being bonded to soil particles during drying.