Earthworm populations in dryland cropping soils under conservation-tillage in south australia

Abstract

The seasonal abundance of earthworms and their vertical distribution were studied in two adjacent fields, sown annually in an alternating cereal-legume rotation, with minimal cultivation and stubble-mulching. The introduced species Aporrectodea trapezoides, Microscolex dubius and M. phosphoreus were concentrated in the upper 10cm of soil for 90–150 days following the onset of autumn rains, but were not active in the top 60 cm after the rainfall declined in spring and throughout the dry summer. Densities of up to 430 worms m −2 with a biomass of 111 g m −2 were recorded in the wetter months. M. dubius was the dominant species in both fields in both years. Differences in abundance, biomass and age-structure are discussed in relation to soil moisture, pH, carbonate, organic C and N, and to the phase of the crop rotation. The two fields have similar soils, similar cropping history and productivity, but one field had consistently higher earthworm numbers and biomass throughout 1988 and 1989. In each field the average size and total biomass were higher, growth rate higher and adults relatively more abundant under cereal than under the alternate legume phase.