Increasing nitrogen application is predicted to alleviate the effects of climate warming on maize yield reduction and maintain the dietary supply of wheat and maize protein

High temperature is known to reduce crop yield, while increased nitrogen (N) application will increase crop grain and protein yields to a certain extent. However, there are few studies on the effects of different N application treatments on crop yield and protein under climate warming in different wheat-maize rotation cultivation sites. Therefore, by utilizing the APSIM model, we investigated crop yield, yield components, grain N contents, and biomass N content across 71 key sites of wheat-maize rotation cultivation systems in China. Four N treatments of 0, 90, 180 and 270 kg N ha^–1 (N0, N90, N180 and N270) were applied before sowing in both wheat and maize seasons. The APSIM model was calibrated and validated using data of yield and grain N content. We predicted regional differences in crop yield and grain N content under a warming 2°C scenario. There were regional differences in the effects of increased N application treatments and warming 2°C on wheat and maize yields, yield components and grain N contents. Increased N application improved maize 1000-grain weight and wheat grain number, and consequently affected crop yield and grain N content but reduced N translocation from plants to grains (NHI), especially in areas with more precipitation in wheat season and higher temperature in maize season. Warming shortened the duration of the reproductive growth period in maize by 6.2–9.5 d but lengthened it in wheat by 9.1–16.5 d. Furthermore, warming reduced maize yield mainly by decreasing maize 1000-grain weight and improved wheat yield mainly by increasing 1000-grain weight. Warming improved wheat grain N content and NHI under different N application treatments, especially in Shandong, Guanzhong, and Henan regions (0.86–1.98 kg ha^–1 and 0.01–0.27, respectively). However, warming reduced maize yield, grain N content and NHI by 4.1 %–10.9 %, 1.5 %–6.8 % and 0.7 %–6.1 %, respectively, under different N application treatments except in Guanzhong. Additionally, increasing N application rate could alleviate the negative effects of warming on maize yield and grain protein production. In 2050–2067 maintaining historical plantation area, the regional total maize protein supply population was projected to reduce by 962.17 and 388.95 million people under N application of N180 and N270 kg N ha^–1, respectively, compared with 2000–2017. The findings would provide scientific basis for N management strategies in wheat-maize rotation planting areas of China under climate warming.