Differences in nitrogen release from surface and incorporated plant residues by two endogeic species of earthworms (Lumbricidae) in a red–brown earth soil in southern Australia

Two endogeic earthworms, Aporrectodea rosea and A. trapezoides (Lumbricidae), occur in soils used for grain production in southern Australia. A glass-house experiment evaluated the influence of A. rosea and A. trapezoides on the release and availability of nitrogen (N) in a red–brown earth soil, which is very common in the region. This soil had been treated with sub-terranean clover or wheat residues (both either added to the soil surface or mixed through the soil at the start of the experiment), wheat residues incorporated into the soil 5 years earlier, or no residue amendment (control). The survival and biomass of earthworms varied with amendment. Most notably, the biomass of individual A. trapezoides was greater in the presence of sub-clover (probably better quality food) and when in mixed culture with A. rosea (effectively a reduction in the density of A. trapezoides). A. trapezoides increased soil inorganic N in the presence of surface-applied sub-clover residues, but A. rosea did not. Incorporation of sub-clover residues further increased soil N in the presence of A. trapezoides, but not A. rosea. Wheat residues immobilised N when incorporated, but A. trapezoides reduced this immobilisation. A. rosea did not. No earthworm effects were detected in the control and old wheat residue treatments. The work suggests that A. trapezoides has the potential to significantly increase the availability of N in a soil commonly used for grain production across southern Australia.