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 bioma ss and inorganic N farms was studied for more than 2 years at three experim ental 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 w ere 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, a nd 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 mo re humid sites (mid- and high-elevation sites) showed an increase in most o f 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 a nd clay. This resulted in faster organic matter turnover when climatic cond itions were favourable. The presence of earthworms greatly increased the qu antity of inorganic N (mainly NH4+) in the soils and enhanced the release o f N from the N-15-labelled decomposing material and the native organic matt er, compared to soil without earthworms.