Adopting nitrogen deep placement based on different simulated precipitation year types enhances wheat yield and resource utilization by promoting photosynthesis capacity

Simultaneously increasing the crop yield and resource utilization efficiency in winter wheat is challenging. The deep placement of nitrogen (N) fertilizer is considered as an effective strategy to address this problem. However, it is unclear whether deep fertilizer application can promote root growth to improve the photosynthetic capacity, and then contribute to improvements in the yield and resource utilization efficiency. In the present study, a two-year simulated precipitation experiment was conducted in a semi-humid region to assess the effects of N fertilizer placement depths comprising 5 cm (D5, conventional surface fertilization), 15 cm (D15), 25 cm (D25), and 35 cm (D35) under three precipitation year types simulated during the winter wheat growth (dry year = 125 mm, P125; normal year = 200 mm, P200; wet year = 275 mm, P275) on the root traits and their distribution with soil nitrate N, leaf functional characteristics, resource utilization, and yield in wheat. Deep N placement increased the root surface area density (RSD) and root volume density (RVD) in the 0–100 cm soil layer during senescence by 1.0–22.7% and 0.2–7.6% compared to D5 in the dry and normal years, respectively. Compared with D15 and D5, deeper N placement (D25 and D35) significantly inhibited the RSD and RVD decrease during senescence in the 60–100 cm layer (0.1–0.2%) in the wet year (p < 0.05), but exacerbated that in the 0–60 cm soil layer (1.3–1.4%). P125D35, P200D25, and P275D15 increased the net photosynthetic rate by 9.3%, 7.5%, and 1.7%, respectively, compared with D5 under the same precipitation type, and the maximum quantum efficiency of PSII by 2.3%, 1.3%, and 0.4%. Under the same precipitation type, P125D35, P200D25, and P275D15 significantly increased the biomass, N translocation, water-N utilization efficiency, and yield in wheat compared with the other N placement depths (p < 0.05). The soil NO3–-N contents in the 0–100 cm layer did not differ significantly under D15 and D5 in the wet year, but the soil NO3–-N concentration in the deep layer (80–100 cm) was significantly greater under D35. We demonstrated that N fertilizer placement at depths of 31.3, 24.3, and 18.0 cm in dry, normal, and wet years, respectively, can enhance yield and water/N utilization in wheat by improving the photosynthesis and root growth. This management practice can replace conventional surface fertilization to obtain high yields and efficiently utilize resources in the semi-humid regions.