Amplitude and frequency of wetting and drying cycles drive N2 and N2O emissions from a subtropical pasture

Changes in amplitude and frequency of wetting and drying cycles in pasture systems due to climatic variation and irrigation management are likely to affect magnitude and partitioning of N2 and N2O emissions. This study investigated the effects of irrigation frequency of N2 and N2O emissions from an intensively managed pasture in the subtropics. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (Low-Frequency) or split into four applications (High-Frequency). To test for legacy effects, a large rainfall event was simulated at the end of the experiment. Over 15 days, 7.9 ± 2.7 kg N2+N2O-N ha-1 was emitted on average regardless of irrigation frequency, with N2O accounting for 25% of overall N2+N2O. Repeated, small amounts of irrigation produced an equal amount of N2+N2O losses as a single, large irrigation event. The increase of N2O emissions after the large rainfall event was smaller in the High-Frequency treatment, shifting the N2O/(N2O+N2) ratio towards N2. Our findings suggest that reduced soil-gas diffusivity predominantly drives N2O and N2 emissions following large wetting events, while microbial O2 consumption largely drives N2O and N2 emissions after small, repeated wetting events in high N turnover pasture soils. The abundance of marker genes for N cycling did not differ between treatments, indicating that N and C availability, not gene abundance determined magnitude and N2O:N2 partitioning after rainfall.

FRIEDL Johannes;  DELTEDESCO Evi;  KEIBLINGER Katharina;  GORFER Markus;  DE ROSA Daniele;  SCHEER Clemens;  GRACE Peter;  ROWLINGS David; 

2022-12-05

SPRINGER

JRC127726

0178-2762 (online),   

https://link.springer.com/article/10.1007/s00374-022-01646-9,    https://publications.jrc.ec.europa.eu/repository/handle/JRC127726,   

10.1007/s00374-022-01646-9 (online),