Effect of climate, soil tyne and earthworm activity on nitrogen transfer from a nitrogen-15-labelled decomposing material under field conditions

N transfer from N-15-labelled decomposing material into the microbial biomass and inorganic N farms was studied for more than 2 years at three experimental sites differing in climatic conditions and earthworm abundance. The N-15-labelled decomposing material was mined with low-elevation soil (LES), mid-elevation soil (MES) and high-elevation soil (HES). The amended soils were put into two kinds of plastic cylinders closed on both sides with nets preventing (0.1 cm mesh) and allowing (0.5 cm mesh) access by earthworms, and were buried in soil (20 cm depth) to monitor the transfer of N from the N-15-labelled decomposing material. Climate and soil type play an important role in the release of N from decomposing material. LES transplanted to more humid sites (mid- and high-elevation sites) showed an increase in most of its biological activities (N atom % excess, and microbial biomass C and N). Furthermore, LES was a sandy soil in which the N-15-labelled decomposing material was less bound than in IVIES and HES, which contained more silt and clay. This resulted in faster organic matter turnover when climatic conditions were favourable. The presence of earthworms greatly increased the quantity of inorganic N (mainly NH4+) in the soils and enhanced the release of N from the N-15-labelled decomposing material and the native organic matter, compared to soil without earthworms.