SEASONAL-CHANGES IN THE ABUNDANCE OF EARTHWORMS (ANNELIDA, LUMBRICIDAE AND ACANTHODRILIDAE) IN SOILS USED FOR CEREAL AND LUCERNE PRODUCTIONIN SOUTH AUSTRALIA

The abundances of the introduced earthworms, Aporrectodea rosea, A. tr apezoides, Microscolex dubius and M. phosphoreus were monitored monthl y in the top 30 cm of soil at three farms used for cereal and lucerne production in South Australia. The farms bad approximately 500 mm annu al rainfall. Total earthworm densities of up to 303 m-2 were recorded, with the Aporrectodea spp. far more abundant than the Microscolex spp . Highest numbers were found in winter and early spring, when the soil s were wettest (water suction potential <approx. 150 kPa) and the majo rity of worms were present in the top 10 cm of soil. During the drier months of the year, most worms were found below 10 cm depth. Adults wi th mature clitella were restricted to winter and spring. Juveniles and adults (with regressed clitella) of Aporrectodea spp. survived summer .