Abstract:The effects of different fertilization on rice growth, nitrogen use efficiency and loss were studied by in-situ and micro-area isotope experiments, and the mechanism was explored through the nitrogen transformation. The results show as follows:1) Compared with conventional surface application (CT), urea deep placement (DT) and urea deep application combined with organic addition (DT+M) significantly decrease 15N -NH3 emission. The emission factors in DT and DT+M are 0.19% and 0.37%, which are 95.8% and 91.7% lower than that in CT, respectively. 2) Compared with CT, nitrogen deep application significantly increases the uptake of 15N from rice plant and root, and reduces the loss of 15N. DT+M has the lowest 15N loss among the different fertilizer treatments, which is 48.7% lower than that of CT. 3) Nitrogen deep application can enhance the fixation of soil NH4+-N and increase nitrogen use efficiency. DT and DT+M increase nitrogen recovery efficiency by 69.8% and 57.1% compared with CT, respectively. In addition, DT also contributes to the increase of rice yield, but it is affected by environmental conditions. By contrast, DT+M gives a stable increase of rice yield.