SHORT-TERM EFFECTS OF TILLAGE AND STUBBLE MANAGEMENT ON EARTHWORM POPULATIONS IN CROPPING SYSTEMS IN SOUTHERN NEW-SOUTH-WALES

The effects of tillage and stubble management on the population distribution of earthworms were examined under wheat on a red-earth soil at Harden and under canola on a red-brown earth at Temora in the wheatbelt of southern New South Wales. At Harden, a five-year pasture had been followed by a conventionally cultivated oat crop in the year before the experiment. At Temora, a six-year pasture immediately preceded the experiment. Tillage treatments at Temora, and tillage and stubble treatments at Harden, were established during February-May 1990 and earthworm populations were measured in September. A number of earthworm species (Aporrectodea trapezoides, Microscolex dubius and M. phosphoreus) were present at both localities, but the introduced species A. trapezoides made up 97-99% of the earthworms collected. Earthworms were substantially more abundant at Temora (425 m(-2)) than at Harden (122 m(-2)). At Temora there was no effect of the intensity of tillage (4, 1 or 0 passes prior to sowing) on earthworm numbers. Earthworm densities were reduced in waterlogged soil. At Harden the direct-drill (DD) plots had a greater population density and biomass of earthworms and cocoons than the tilled plots. The size (mean weight) of adult earthworms, and the number of cocoons per adult, were also greater in the DD plots. However, no differences in earthworm populations were detected between minimum tillage (one cultivation prior to sowing) and stubble incorporation (three cultivations prior to sowing). On DD plots, burning stubble resulted in significantly smaller adult earthworms, a lower density of cocoons and a lower mean number of cocoons per adult than in the unburnt plots, but the differences in numerical abundance and in biomass were not statistically significant. Similarly, plots which had standing stubble contained fewer and smaller adults than those in which stubble was bashed and in close contact with the soil. There was a strong positive correlation between earthworm biomass and the amount of stubble present on the surface of the plots at the beginning of the winter (r(2) = 0.64, P < 0.01). The contrasting effects of tillage at the two sites and the impact of stubble management on earthworms are discussed in terms of the effects of recent paddock history and management practices on the amount, quality and distribution of suitable organic food for earthworms. The influence of these factors is reflected in the number, biomass and reproductive performance of the earthworms.