Populations of soil organisms under continuous set: stocked and high intensity - short duration rotational grazing in the central tablelands of New South Wales (Australia).

Grazing management practices modify soil structure, which, in turn, alters the behaviour and population dynamics of soil-inhabiting organisms. Monitoring of changes in abundance and richness of soil organisms is vital in determining the sustainability of grazing regimes. In this paper, populations of soil organisms were compared--using abundance and population trends as an indicator of diversity--in two different grazing practices (a) conventional, set stocked (SS) grazing regime and (b) high intensity-short duration (HI-SD) grazing regime) and an ungrazed control (C). A thorough sampling of earthworms and arthropods, and an assay of soil microbial biomass and respiration was made in Spring 2004 (September-November), after a pilot sampling of earthworms and arthropods in Autumn 2004 (March-May). Earthworm numbers were found to be unaffected by grazing regimes, however, microarthropod abundance at 0-10 cm soil depth was significantly higher in soil of the HI-SD grazing regime and in the ungrazed control, when compared with set stocking. Microbial biomass and respiration did not differ across treatments. Overall, our results indicate that arthropod abundance reflects the changes impacting on soil structure as a consequence of grazing practice. Evaluation of earthworm populations was not found to be useful in discriminating between the two grazing regimes, because the earthworm numbers were principally affected by rainfall.