Nitrogen Mobilization by Earthworms in Limed Peat Soils Under Picea sitchensis

Liming (at 2.5 or 10 t ha-1) of peat taken from under a Sitka spruce stand reduced mortality and weight-loss of five earthworm species, measured over 8 wk. In limed treatments, least population biomass was lost by Aporrectodea caliginosa, A. longa and Lumbricus terrestris. A. caliginosa was the only species to gain any weight in any treatment. All earthworm species increased the amount of N released in leachates from limed and unlimed peat. Nitrate-N release was substantially greater (by up to 50-fold) in treatments with lime and earthworms than with earthworms alone. Aporrectodea caliginosa was the most suitable species of those tested for inoculation into limed deep peat soils under P. sitchensis to improve rates of N mineralization. Aporrectodea caliginosa in limed soil significantly increased leachate N release (to 60 kg ha-1 yr-1) compared with untreated (19 kg ha-1 yr-1), and limed soils (36 kg ha-1 yr-1). Ammonium-N and NO3--N mobilized by addition of earthworms plus lime appeared to be taken up by living roots of P. sitchensis. This increased mineralization can be expected to lead to enhanced tree growth. -from Authors