Abstract:Suitable pH and oxy-reduction conditions in paddy induced by flooding supply optimal conditions for diazotrophs to do N2 fixation. Paddy biological N2 fixation makes paddy be different from upland. Paddy can sustain certain productivity under no N fertilization, while upland productivity decreases year by year. Along with an increase of chemical active N application, environment becomes severely polluted. To secure food production and decrease environmental pollution, biological N2 fixation is urgently to be increased to reduce chemical N fertilizer application. In order to better explore capacities of paddy biological N2 fixation, we make the reviews on progresses of quantification techniques, controlling factors, enhancement techniques and perspectives in paddy N2 fixation. We hope this review can offer some helps for further studies on paddy N2 fixation.