Abstract: Maize (Zea mays L.) is the largest grain crop in China. Realizing super-high-yield (≥12 000 kg ha^-1) of summer maize plays an important role in ensuring the country food security. However, there exist some problems in summer maize production such as excessive dosage and unreasonable period of nitrogen application, which hinders the realization of super-high-yield. In order to increase the use efficiency of fertilizer and grain yield of summer maize, field experiments were conducted and the effects of postponing N application on nitrogen absorption, use efficiency of nitrogen fertilizer and grain yield in summer maize were studied. The results showed that yield was increased by 9.62%–15.95% by applying nitrogen fertilizer. Compared with conventional fertilizer application, postponing N application increased grain yield by 2.27%–5.33%. The N absorption proportion after silking stage was 40.30%–47.78% of the total, so it is important to provide maize plants with sufficient N in later growth stage for realizing super-high-yield. It was indicated that postponing N application could promote N absorption and accumulation of super-high-yield summer maize at later stage, decrease N transfer efficiency in stem and leaf, increase activity of nitrate reductase and content of free amino acids in ear leaf at filling stage, and raise protein yield of summer maize. In comparison with conventional fertilizer application, the N fertilizer utilization rate and N fertilizer agronomy efficiency were increased by 1.88%–9.70% and 0.96–2.21 kg kg^-1 respectively by postponing N application. The highest yield and nitrogenous fertilizer use efficiency were obtained by applying 30% of nitrogen fertilizer at seedling stage and trumpeting stage respectively and 40% of nitrogen fertilizer at silking stage.

Key words: Summer maize, Super-high-yield, Postponing N application, Yield, Nitrogen absorption, Nitrogenous fertilizer efficiency