Objectives Excessive nitrogen (N) fertilization in maize is concerned in the North China Plain. Winter wheat–summer maize rotation is the most common agricultural production system in this area. For enhancing maize production and protecting the environment, it is necessary to reduce fertilizer input and to increase fertilizer use efficiency. The objective of this paper was to investigate maize grain yield, N use efficiency, root morphology and inorganic nitrogen characteristics in rhizosphere soils of reducing application rate of N fertilizer to provide technical basis for rational application of nitrogen fertilizer in winter wheat– summer maize crop rotation systems.

Methods A field experiment was conducted on fluvo-aquic soil in Hengshui City, Hebei Province. The cropping system was winter wheat−summer maize rotation. The experiment was lasted for three years from 2008 to 2010. For winter wheat, the designed four N application rates were 0, 180, 225 and 300 kg/hm². After wheat harvest, summer maize was planted without tillage, and the N rates in above four treatments became 0, 144, 180 and 240 kg/hm² in turn. The grain yields, total N uptake and N content in maize shoots were investigated. The contents of soil NO₃^–-N and NH₄⁺-N in rhizosphere were analyzed. Root analysis system WinRHIZO was used to determine the root length and diameter.

Results Compared to N240, the rate of 144 and 180 kg/hm² did not significantly affect maize grain yield, total root length, average root diameter and soil NO₃^–-N and NH₄⁺-N contents in rhizosphere soils during three years’ period, however, obviously increased N utilization and recovery rate. Maize yield and NO₃^–-N and NH₄⁺-N content in non-rhizosphere soils started to decline in treatments of N0, N144 and N180 in the third season. Except for the bell-mouthed stage of maize in 2008, the NO₃^–-N contents in the rhizosphere soils were lower than in the non-rhizosphere soils. The of NH₄⁺-N contents in rhizosphere soils were higher than in the non-rhizosphere soils at maize tasseling stage in 2008, while at maize harvest stage, the amounts of NH₄⁺-N in rhizosphere soils were lower than in the non-rhizosphere soils. When less N fertilizer was applied, the contents of NH₄⁺-N in rhizosphere soils presented no significant change. Pearson correlation analysis showed that grain yield significantly and positively correlated with shoot total N uptake after bell-mouthed stage in 2008 and 2009 year, while in 2010, it was only significantly correlated with shot N content in the seedling and harvest stage. NO₃^–-N content in rhizosphere soil significantly correlated with grain yield in 2009 year. The contents of NO₃^–-N in non-rhizosphere soils significantly correlated with the yield except for bell-mouthed stage in 2009 year.

Conclusions Under the intensive rotation system of winter wheat and summer maize in North China Plain with high soil fertility, the yield and root development of maize, and the contents of NO₃^–-N and NH₄⁺-N in the rhizosphere soils did not show significant variation, but N utilization increased significantly when the N fertilizer input was reduced by 25% or even 40% in maize season. In the third year. maize yield and inorganic nitrogen content in non-rhizosphere soils started to decline. As a result, It is suggested that it would be available to reduce the N input by 40% in the short-term winter wheat–summer maize crop rotation systems in high-fertility areas of Hebei Province, continued reduction of nitrogen fertilizer needs further research.