Impact of crop management factors in conservation tillage farming on earthworm density, age structure and species abundance in south-eastern Australia

Cropping practices commonly used in conservation tillage can potentially im pact on earthworm abundance and distribution. Management practices associat ed with conservation tillage fanning for cereals such as stubble retention and management, greater utilization of herbicides, and soil acidity amelior ation were assessed for their influence on earthworm density, age structure , and species abundance at a total of seven sites on Chromic Luvisols in no rth-eastern Victoria, Australia. Earthworms were sampled from the surface s oil (0.1 m(2) x 0.1 m deep) at the end of the cool wet season (August-Septe mber) when species tend to concentrate at this soil depth. In three six-yea r experiments, crop management practices that retained stubble as a surface mulch for successive years supported consistently higher densities of eart hworms, followed by retained stubble left standing, burning stubble, and in corporation of stubble. The latter reduced earthworm densities by an averag e of 53%, compared to the mulched system. This trend was consistent across texturally different soils. Autumn application of postemergent herbicides f or two consecutive years, at double recommended rates, was associated with significant increases in earthworm densities (by 10-124%) the following spr ing, compared to the recommended rate. Herbicide application had no influen ce on earthworm species richness, Although the effect of increasing soil pH on earthworm numbers was variable, lowering the pH consistently lowered ea rthworm densities (by 60%). No clear trend was observed in earthworm popula tion age structure at any of the sites. Overall, reduced soil disturbance a nd increased inputs of crop residue at the soil surface, although having li ttle effect on diversity of species, are conducive to increasing earthworm populations in conservation tillage cropping practices in north-eastern Vic toria. (C) 1999 Elsevier Science B.V. All rights reserved.