The occurrence of earthworms in the wheat belt of Western Australia in relation to land use and rainfall

Abstract

The distribution of earthworms in a large portion of the wheat-belt of Western Australia was documented in August 1979. Four species were found, three of which are introduced. Two of these (Allolobophora trapezoides Duges, Microscolex dubius (Fletcher)) were widespread. The occurrence of earthworms was related to land use: the percentage of gardens, pasture, cultivated and uncleared sites examined which had earthworms present was 100, 54, 18 and 23% respectively. There was no relation between the proportion of pasture sites occupied by earthworms and rainfall zone. Food supply, and not rainfall, appears to be the major determinant of distribution of earthworms in the wheat-belt. Both Allolobophora trapezoides and Microscolex dubius jointly occur in more garden samples than pasture samples; in pasture one or the other species tends to occur alone. Four laboratory experiments were conducted. In two, earthworms (Allolobophova trapezoides, Eisenia foetida) lost weight over 8 weeks when kept in virgin and cultivated wheat-belt soils with adequate moisture, suggesting that the nutrient status of such soils is too poor for earthworms. In the other two experiments, in which adequate food was supplied in a confined space, earthworms did not persist for 8 weeks where soil water was only 10% or 20% of pore space. Most survived in soil where moisture was 30-100 % of pore space, indicating that these earthworms can tolerate a broad range of soil moisture regimes.