Effects of earthworms on cation and phosphate mobilisation in limed peat soils under Picea sitchensis

Aporrectodea caliginosa was successfully introduced into limed peat monoliths in field lysimeters under a stand of Picea sitchensis which had been fertilised with P and K at 75 and 100 kg ha-1 5 years previously. Total earthworm biomass was sustained over the 12 months of the experiment in the limed treatments, whereas only 3% remained in the treatment without lime. Earthworm cocoons were produced in the limed treatments only. Aporrectodea caliginosa in limed soil significantly increased leachate fluxes to lower soil horizons of K+ (to 35 kg ha-1 year-1), Ca2+ (to 303 kg ha-1 year-1) and Mg2+ (to 19 kg ha-1 year-1), compared with untreated controls (19, 8 and 4 kg ha-1 year-1 respectively). These increased leachate Ca2+ and Mg2+ values were also significantly greater than from limed-only soils (56 and 8 kg ha-1 year-1, respectively), and treatments in which earthworms alone were added (10 and 6 kg ha-1 year-1, respectively). Potassium and Mg2+ mobilised by the addition of earthworms plus lime appeared to be taken up by living roots of P. sitchensis. There was no effect of any treatment on phosphate release.