Effect of straw incorporation and nitrification inhibitor on nitrous oxide emission in various cropland soils and its microbial mechanism

Nitrification inhibitor and straw incorporation are widely used to improve crop nitrogen use efficiency in agricultural soil, but their effects on nitrous oxide (N 2 O) emission across different soil types and the microbial mechanisms remain less understood. In this study, we used controlled experiment and DNA-based molecular analysis to study how nitrification inhibitor (dicyandiamide, DCD) and straw incorporation affect soil nitrogen balance, N 2 O emission and microbial nitrifiers/denitrifers in three distinct agricultural soils (the black, fluvo-aquic and red soils) across China. Both DCD and straw incorporation improved nitrogen balance by increasing NH 4 + and decreasing NO 3 - in all soils. DCD tended to decrease N 2 O emission from all soils especially the fluvo-aquic one, while straw incorporation reduced N 2 O emission only in the fluvo-aquic soil but increased N 2 O emission in the other two especially the red soil (by ∼600%). T-RFLP analysis revealed that the denitriers community structure are distinct among the three soils but was not strongly affected by DCD or straw incorporation. qPCR analysis revealed that DCD or straw incorporation had no significant effect on nitrifier abundance but increased nitrous oxide reductase nosZ gene abundance in the black/fluvo-aquic soil rather than the red soil. Structural equational modelling further confirmed that, when accounting for treatments and soil properties, nosZ gene abundance is the only biological factor significantly determined N 2 O emission in different soil types. Taken together, our work advanced the knowledge on the agricultural practices and N 2 O emission in cropland soils, suggesting that straw incorporation may not be a good choice for the red and black soil areas; management practices should be used as per soil type to balance between nitrogen use efficiency and N 2 O emission.