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Quantitative understanding of how fertilizer N affects tiller development is essential for simultaneously achieving high yield and high N use efficiency in wheat (Triticum aestivum L.) production. A 3-yr field experiment was conducted on the North China Plain during 2015-2017, with winter wheat grown at five fertilizer N rates (0-300 kg ha −1 ). The highest grain yield (∼9 Mg ha −1 ) was obtained at the optimized N rate (on average 160 kg ha −1 , determined by subtracting the soil NO 3 − content from estimated N target values) and attributed to the high spike number, which was further contributed by the main stem (MS) and the fertile first tiller (T1). Greater N application than the optimized rate did not further increase grain yield but increased the biomass and N concentration of other tillers that were unproductive. The critical plant aboveground N concentrations (2.81% at stem elongation stage [Zadoks Growth Stage, GS 31] and 1.95% at anthesis (GS 64) and critical root-zone soil mineral N content (N min ) (74 kg ha −1 at GS 31 and 129 kg ha −1 at GS 64) for the attainable maximum stem number (1578 m −2 at GS 31 and 944 m −2 at GS 64) were quantified in this high-yieldingsystem. The critical plant aboveground N concentrations for achieving the maximal biomass of stem were also established to be 2.72% at GS 31 and 1.53% at GS 64, respectively. At these critical levels, the maximal biomass of MS and T1 were obtained without increasing the growth of the other tillers that were unproductive. Our results showed that high yield of winter wheat can be achieved by increasing the number of productive stems and the biomass per productive stem through optimizing the rootzone N min and plant N concentrations.

Sustainably feeding the growing human population requires improvements in both soil quality and nitrogen (N) management. However, in response to N fertilizer addition, whether soil quality will be optimized at N application rates that maximize yields is rarely explored from a long‐term perspective. We conducted a 9‐year field experiment to examine agronomic and soil quality indices in a wheat (Triticum aestivum L.)/maize (Zea mays L.) double cropping system. Optimal nitrogen rates (ONR) were determined by in‐season soil NO3−‐N testing. Other treatments included control plots, 50–70% ONR, 130–150% ONR, and local farmers' N practices (FNP). The ONR increased grain yield by 10.5% in comparison with the 50–70% ONR treatment and achieved yields comparable to the 130–150% ONR treatment. The ONR treatment reduced the applied N fertilization rate by 38.5% in comparison with FNP levels but without any yield losses. After N fertilization for 9 years, soil organic carbon (SOC) stocks, C sequestration rates, and soil microbial biomass C were the highest with the ONR treatment. Relative to the control, the ONR treatment significantly increased the weight diameter of soil water‐stable aggregates, reduced the richness and diversity of fungi, and reduced the richness of bacteria in comparison with the FNP treatment. Furthermore, the soil microbial community structure had a significant relationship with the SOC, organic C input, and soil inorganic N content, which was ascribed to the driving of N management strategy. These results highlight the importance of the optimization of N management to produce high grain with less N fertilizer input in agricultural systems while concurrently promoting soil quality and providing benefits to the microbial community.

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