Abstract: 【Objective】The effect of humic acid on yield, nitrogen fertilizer utilization and economic benefit of summer maize was studied in order to provide a theoretical basis for increasing in yield of maize benefited from nitrogen fertilizer and reducing nitrogen fertilizer pollution to the ecological environment.【Method】A field experiment was started in 2014 in Boai county, Henan province where the cropping system was winter wheat and summer maize rotation and the soil was Fluvo-aquic soil. The experiment included 5 treatments: No N fertilizer (single PK fertilizer), conventional fertilization, conventional fertilization+humic acid, conventional fertilization and nitrogen reduction 15%+humic acid, conventional fertilization and nitrogen reduction 30%+humic acid, and the effects of different nitrogen application on the growth, yield and yield components of summer maize were studied. The effects of different parts of plants on nitrogen uptake, accumulation and distribution, nitrogen use efficiency and economic benefit of summer maize under different fertilization levels were analyzed.【Result】Compared with the conventional fertilization treatment, application of P, K fertilizers decreased the stem diameter, ear length, ear diameter, and leaf area index by 4.61%, 8.55%, 6.20%, 26.91%, bald length increased by 21.60%. Compared with single application of P, K fertilizer, conventional fertilizer treatment increased the single grain number per ear, 100-grain weight and yield by 8.01%, 10.85%, and 44.45%, respectively. The nitrogen content and nitrogen accumulation in grain were decreased by 6.67% and 54.07%, in addition, the conventional fertilization treatment increased the production value, net income and input-output ratio by 44.45% and 59.80%, and 43.84%, respectively, showing that nitrogen fertilizer can promote maize plant growth, improve each index of biological characteristics, greatly improve the summer maize, increase the concentration and accumulation of each part of maize plant, and further to improve the maize output value, net income and input-output ratio. Compared with the conventional fertilization treatment, the combination of humic acid and fertilizer could effectively improve the agronomic traits of summer maize, improve the yield of summer maize, promote the accumulation of nitrogen in plant and improve the utilization rate of nitrogen fertilizer. The effect of conventional fertilization with reduced nitrogen by 15% plus humic acid treatment was the best compared with the conventional fertilization, and the plant height, stem diameter, ear length were increased by 3.73%, 2.30%, and 0.12%, the length of bald decreased by 22.45%, the yield increased by 12.88%, grain nitrogen content, the accumulated amount of grain nitrogen, the total accumulated nitrogen amount of aerial part, and the harvest index were increased by 2.68%, 25.98%, 10.70%, and 13.79%, respectively. Nitrogen agronomic efficiency, nitrogen partial productivity, nitrogen contribution rate, and nitrogen utilization rate increased by 57.46%, 28.84%, 22.23%, and 59.86%, respectively. Net income increased by 8.66%. In the conventional fertilization with reduced nitrogen fertilizer by 15% and plus    3 000 kg·hm^-2 of humic acid could effectively increase the yield of summer maize, improve nitrogen use efficiency; but 30% reduction in nitrogen led the output and income of summer maize decreased.【Conclusion】Nitrogen fertilizer has positive effects on maize growth and development, not only can promote the growth of summer maize, but also can increase the yield, improve the nitrogen content in different parts of plant, promote the absorption and distribution of nitrogen, improve the utilization rate of nitrogen fertilizer. However, excessive or small amount of nitrogen fertilizer can reduce economic benefits and ecological environment benefit. On the basis of the application of humic acid, the appropriate amount of nitrogen fertilizer could get higher production value and income. The conventional fertilization with nitrogen reduced by 15% plus 3 000 kg·hm^-2 humic acid is the best fertilization mode in the study area. At the same time, while this fertilizer application method not only can promote the growth and development of summer maize, but also can improve the yield and composition of summer maize, promote nitrogen absorption and utilization of plants, improve the utilization of nitrogen fertilizer, increase the output value of summer maize and net income. It is of great significance to realize the high yield and high efficiency, resource conservation and ecological environment protection of modern agricultural production.

Key words: humic acid, summer maize, nitrogen fertilizer, nitrogen fertilizer use efficiency, yield