Gross Nitrogen Transformations and Related Nitrous Oxide Emissions in an Intensively Used Calcareous Soil

A better understanding of the internal N cycle in agriculturally used soils is crucial for developing sustainable and environmentally friendly N fertilizer management and to propose effective N2O mitigation strategies. The present laboratory study quantifies gross nitrogen transformations in an intensively used agricultural soil of the North China Plain (NCP). It also elucidates the role of nitrification and denitrification in the emissions of the greenhouse gas N2O. In the lab, soil samples adjusted to a water-filled pore space (WFPS) of 40 or 60% were spiked with (NH4NO3)-N-15, (NH4NO3)-N-15, or (NH4NO3)-N-15-N-15 and incubated at 20 degrees C for 10 d. One subset of the samples was amended with glucose. The size and N-15 enrichment of the mineral N pools and N2O fluxes were determined at intervals of 0 to 10 d. The studied calcareous soil showed a very rapid nitrification of the applied NH4+, which disappeared during the first 3 d. Glucose enhanced mineralization of native soil organic matter (SOM), stimulated dissimilatory nitrate reduction to ammonium (DNRA), and promoted the immobilization-remineralization cycle. Throughout the incubation, nitrification, and denitrification Occurred simultaneously. Nitrification was the dominant N2O-producing process and contributed 83.0 to 95.4% to the totally emitted N2O in the non-glucose soils. In contrast, the N2O emitted from (NO3-)-N-15 pool increased after adding glucose, indicating that denitrification was C-limited in the studied soil.