Abstract: 【Objective】 To clarify the effect of nitrogen fertilizer and density interaction on spring maize inferior kernels sink capacity and sink activity,in order to provide a theoretical basis for tapping the potential of spring maize yield.【Methods】With three nitrogen fertilizer amounts and five density levels,15 treatments were set up using Zhengdan 958 and Xianyu 335 as experimental materials. The sink activity,individual sink capacity,population sink capacity and ear abortion rate of maize inferior kernel were monitored on a regular basis.【Results】Under the interaction of nitrogen fertilizer and density,the sink activity（SAI）of spring maize inferior kernel grew first and then declined with the process of grain filling,peaking at 24 days after pollination. The enzyme activity of inferior kernel under the densities of 45 000,60 000 and 75 000 plants/hm² were significantly higher（P<0.05）than those under the densities of 90 000 and 105 000 plants/hm². With nitrogen application of 150 and 300 kg/hm²,the enzyme activity of inferior kernel was significantly higher than that without nitrogen application. When planting density reached 75 000 plants/hm²,increasing the density will significantly reduce the maximum SAI activity of inferior kernels. When planting density was less than 75 000 plants/hm²,the SAI activity increased gradually with the increase of nitrogen application. There was significant difference（P<0.05）between no nitrogen application and nitrogen application of 150 and 300 kg/hm². Under the same nitrogen application level,the number of grains per ear decreased significantly as density increased. The difference between low and high density was significant（P<0.05）. Under the same density,the number of grains per ear increased significantly with the increase of nitrogen application. The difference between no nitrogen application and 150 and 300 kg/hm²（P<0.05）nitrogen application was significant（P<0.05）. Under the same nitrogen application level,the number of grains per ear per unit area increased gradually with the increase of density. There was significant difference in the number of grains per ear per unit area between the density of 45 000 and 60 000 plants/hm² and density of 90 000 and 105 000 plants/hm²（P<0.05）. Under the same density,the number of grains per ear per unit area rose with the increase of nitrogen application. The ear abortion rate increased significantly as the density increase. High density ear abortion rate was significantly higher than that of low density（P<0.05）. Increasing nitrogen fertilizer could cut the ear abortion rate significantly. The ear abortion rate differed significantly between no nitrogen fertilizer and 300 kg/hm² under high density（P<0.05）.【Conclusion】By modulating grain sink activity,the nitrogen fertilizer and density interaction altered the spring maize ear abortion rate and individual sink capacity of inferior kernels. The effect was amplified under high density. The application of nitrogen fertilizer could help to mitigate the decline in population sink capacity induced by increased density.

Key words: Nitrogen fertilizer and density interaction, Spring maize, Inferior kernel, Sink capacity, Sink activity