OCCURRENCE OF ENCHYTRAEID WORMS AND SOME PROPERTIES OF THEIR CASTS IN AN AUSTRALIAN SOIL UNDER CROPPING

The population density of enchytraeid worms (Oligochaeta) was monitored on a red earth (Oxic Paleustalf) under cropping in Wagga Wagga, N.S.W. Physical and chemical properties of their casts were compared with those of the bulk soil and soil sampled adjacent to the permanent fenceline. In the autumn and winter period, the worm population was active close to the surface and the highest population (2037 per m(2)) was detected in the direct drilled/stubble burnt treatment. However, this was considerably lower than those reported elsewhere in temperate regions. Worm casts were composite in nature, predominately of 210-500 mu m in diameter which were comprised of smaller spherical subunits (50-100 mu m). The casts were found to be significantly more water stable and higher in total nitrogen than aggregates of the same size range separated from the bulk soil. Porosity of the casts was dominated by spaces between the subunits which were composed of very densely packed clay/silt size particles. Evidence from SEM (scanning electron microscope) suggests that the high stability was due to the presence of cements.