Prior nitrogen fertilization stimulated N2O emission from rice cultivation season under a rapeseed-rice production system

Aims Nitrogenous fertilizer has been recognized as a key factor regulating nitrous oxide (N2O) emissions from agricultural soils. However, the effect of nitrogen (N) fertilization of preceding season on soil N2O emission in subsequent season remain poorly understood. Methods Herein, a field-based study was done to examine the effect of prior N fertilization on N2O 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 (N0-0), N fertilizer (150 kg N ha(-1) y(-1)) was only applied during rapeseed-growing season (N150-0,), N fertilizer (150 kg N ha(-1) y(-1)) was applied in both rapeseed and rice-growing seasons (N150-150), and N fertilizer (150 kg N ha(-1) y(-1)) was only applied during rice-growing season (N0-150). Soil N2O fluxes and the key soil factors (soil available C and N and their ratios, soil temperature and moisture) that further drive N2O 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 N2O 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 N2O emission from rapeseed-growing season, after N fertilization was attributed to high soil mineral nitrogen content (including NH4+-N and NO3--N). N2O efflux was higher when dissolved organic carbon (DOC) to NO3- content ratio (DOC/NO3-) was < 0.5 but lower when DOC/NO3- ratio was > 0.5 for both N150-0 and N150-150 treatments. Pulse N2O 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 N2O fluxes and DOC/NO3- ratio for both N150-150 and N0-150, also revealed that soil available carbon to nitrogen ratio could be a crucial factor regulating peaks of N2O during the rice season. Structural equation model (SEM) displayed the explanation of impact factors on N2O 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/NO3-, influenced by prior N fertilization, play a key role in soil N2O emissions under the RR system.

Automated summary

This study found that nitrogen fertilization in the preceding season can affect soil N2O emissions in the subsequent season in a rapeseed-rice rotation system. The availability of carbon and nitrogen in the soil, as well as the ratio of dissolved organic carbon to nitrate, play key roles in N2O emissions.