Prior nitrogen fertilization stimulated N 2 O emission from rice cultivation season under a rapeseed-rice production system

Aims Nitrogenous fertilizer has been recognized as a key factor regulating nitrous oxide (N 2 O) emissions from agricultural soils. However, the effect of nitrogen (N) fertilization of preceding season on soil N 2 O emission in subsequent season remain poorly understood. Methods Herein, a field-based study was done to examine the effect of prior N fertilization on N 2 O emissions under a rapeseed-rice rotation (RR) system in central China. Treatments were as follows: no N fertilizer was applied in both rapeseed and rice-growing seasons (N 0-0 ), N fertilizer (150 kg N ha −1 y −1 ) was only applied during rapeseed-growing season (N 150-0 ,), N fertilizer (150 kg N ha −1 y −1 ) was applied in both rapeseed and rice-growing seasons (N 150-150 ), and N fertilizer (150 kg N ha −1 y −1 ) was only applied during rice-growing season (N 0-150 ). Soil N 2 O fluxes and the key soil factors (soil available C and N and their ratios, soil temperature and moisture) that further drive N 2 O emissions were determined after N fertilization in preceding and subsequent seasons. Results The application of N fertilizer during the rapeseed-growing season caused a significant increase in soil N 2 O emission from rice-growing season, but no such promotion effect was observed during rapeseed growing season due to N fertilization during prior rice season. Higher N 2 O emission from rapeseed-growing season, after N fertilization was attributed to high soil mineral nitrogen content (including NH 4 + -N and NO 3 − -N). N 2 O efflux was higher when dissolved organic carbon (DOC) to NO 3 − content ratio (DOC/NO 3 − ) was < 0.5 but lower when DOC/NO 3 − ratio was > 0.5 for both N 150-0 and N 150-150 treatments. Pulse N 2 O emission during the rice-growing period was observed due to higher soil DOC content derived from soil organic matter decomposition. The positive correlation between soil N 2 O fluxes and DOC/NO 3 − ratio for both N 150-150 and N 0-150 , also revealed that soil available carbon to nitrogen ratio could be a crucial factor regulating peaks of N 2 O during the rice season. Structural equation model (SEM) displayed the explanation of impact factors on N 2 O emission was 62% during the rapeseed-growing season, while that explanation was 45% during the rice-growing season. Conclusions These results showed that not only labile C and N content, but also soil DOC/NO 3 − , influenced by prior N fertilization, play a key role in soil N 2 O emissions under the RR system.