Split nitrogen application increases maize root growth, yield, and nitrogen use efficiency under soil warming conditions

The increase in soil temperature associated with climate change has introduced considerable challenges to crop production. Split nitrogen application (SN) represents a potential strategy for improving crop nitrogen use efficiency and enhancing crop stress resistance. Nevertheless, the precise interaction between soil warming (SW) and SN remains unclear. In order to ascertain the impact of SW on maize growth and whether SN can improve the tolerance of maize to SW, a two-year field experiment was conducted (2022–2023). The aim was to examine the influence of two SW ranges (MT, warming 1.40 °C; HT, warming 2.75 °C) and two nitrogen application methods (N1, one-time basal application of nitrogen fertilizer; N2, one third of base nitrogen fertilizer + two thirds of jointing stage supplemental nitrogen fertilizer) on maize root growth, photosynthetic characteristics, nitrogen use efficiency, and yield. The results demonstrated that SW impeded root growth and precipitated the premature aging of maize leaves following anthesis, particularly in the HT, which led to a notable reduction in maize yield. In comparison to N1, SN has been shown to increase root length density by 8.54%, root bleeding rate by 8.57%, and enhance root distribution ratio in the middle soil layers (20–60 cm). The interaction between SW and SN had a notable impact on maize growth and yield. The SN improved the absorption and utilization efficiency of nitrogen by promoting root development and downward canopy growth, thus improving the tolerance of maize to SW at the later stage of growth. In particular, the N2HT resulted in a 14.51% increase in the photosynthetic rate, a 18.58% increase in nitrogen absorption efficiency, and a 18.32% increase in maize yield compared with N1HT. It can be posited that the SN represents a viable nitrogen management measure with the potential to enhance maize tolerance to soil high-temperature stress.