RELATIONSHIPS BETWEEN CASTS OF GEOPHAGOUS EARTHWORMS (LUMBRICIDAE, OLIGOCHAETA) AND MATRIC POTENTIAL .2. CLAY DISPERSION FROM CASTS

A laboratory study was conducted to determine the effects of matric po tentials between -25.4 and -2.0 kPa on the mechanical dispersion of fr esh and aged casts produced by Aporrectodea caliginosa, A. rosea, and A. trapezoides. We also examined the effects on dispersion of the matr ic potential at which the air-dried casts were rewetted. Dispersion fr om subsurface casts up to 6 days old and uningested aggregates was inf luenced, but dispersion from fresh casts was not influenced, by the ma tric potential of the soil core from which the samples were collected. Dispersion from subsurface casts and uningested aggregates increased as the matric potential of the soil core increased from -25.4 to -2.0 kPa. Cast dispersion was not influenced by the earthworm species which produced the cast. Little or no clay was mechanically dispersed after the casts had been air-dried and rewetted, and the matric potential a t which casts were rewetted had little influence on dispersion.