The introduction of earthworms to an ameliorated, irrigated duplex soil in south-eastern Australia and the influence on macropores

Abstract

Two species of lumbricid, Aporrectodea caliginosa and Aporrectodea longa and a megascolecid, Eukerria saltenis were introduced, during the winter, to a duplex soil (transitional red-brown earth) ameliorated by either gypsum-enriched slots or beds formed after deep ripping and gypsum application. Some were introduced to areas enclosed by mesh within the slots, others were released in adjacent unenclosed areas. The enclosed areas had the equivalent of 0, 5 or 10 t ha-l of wheat straw on the surface, the unenclosed areas had 5 t ha-1. The enclosed areas were excavated in the spring, 17 weeks after earthworms were introduced. Proportionally more Eukerria adults were recovered than Aporrectodea adults (4040% compared with 10-30%). At 20-45 cm depth, Eukerria adults were four times more common than Aporrectodea. Cocoons and immature forms of Aporrectodea were very common, especially near the surface. Nine months after the introduction, even after a drier than average summer fallow, earthworms were still present. More Eukerria than Aporrectodea adults were found in the sample from the unenclosed areas. The smaller species, Eukerria, (about 1 mm diameter and 30 mm long) may be better adapted to survive in these ameliorated clay soils, but further research is needed. In the enclosed areas, soil macroporosity was unaffected by the 17 weeks with earthworms, but air permeability through the macropores was significantly increased, probably due to the burrows increasing vertical pore connectivity within 0 . 3 m depth.