Influence of earthworms, Aporrectodea spp. (Lumbricidae), on lime burial in pasture soils in south-eastern Australia

The relative abilities of 3 exotic lumbricid earthworms, the endogeic Aporrectodea caliginosa and A. trapezoides and the anecic A. longa, to bury surface-applied lime and help ameliorate soil acidity were measured in cages in 7 pasture soils in south-eastern Australia. All 3 species buried lime, mostly within the top 5 cm of the soil profile, but A. longa buried it deeper than A. caliginosa and A. trapezoides. A. longa significantly increased soil pH at 15-20 cm depth at some sites within 5 months (winter-spring, the earthworm 'season' in the Mediterranean climate of south-eastern Australia). Lime burial varied markedly between sites. These site differences were explained, at least in part, by variations in rainfall. Lime burial increased with earthworm density. A minimum density of 214 A. longa/m(2) was needed to significantly enhance lime burial within one season. Higher densities were required for the other two species. However, per unit of biomass, A. caliginosa and A. trapezoides were generally more able to bury lime in the upper soil layers (2.5-10 cm depth) than A. longa. Agricultural soils in south-eastern Australia are dominated by shallow burrowing species such as A. caliginosa and A. trapezoides. Deeper burrowers such as A. longa are rare. Introduction of A. longa to soils in high-rainfall regions of south-eastern Australia, where it does not presently occur, should enhance lime burial and help reduce soil acidity.