Grain Yield Formation and Nitrogen Utilization Efficiency of Different Winter Wheat Varieties under Rainfed Conditions in the Huang-Huai-Hai Plain

Winter wheat production is threatened by drought stress under rainfed conditions; thus, screening high- and stable-yielding wheat varieties to ensure the sustainable development of wheat production and food security in the Huang-Huai-Hai Plain (HHHP) is vital. In this research, four-year field experiments with twelve winter wheat varieties were conducted during the winter wheat-growing seasons between 2016 and 2020 in order to: (1) screen high- and stable-yielding winter wheat varieties under rainfed conditions, (2) investigate the mechanism of high-yielding wheat yield formation and the relationships among grain-yield formation traits, and (3) investigate the nitrogen utilization efficiency (NUtE) of high-yielding wheat. The results showed that high-yield level wheat varieties (HL; Yannong999, Taimai1918 and Yannong173) obtained a higher average grain yield than medium-yield level wheat varieties (ML) and low-yield level wheat varieties (LL) by 10.1% and 29.0%, respectively. Compared with ML and LL, HL had a higher biomass at anthesis, higher spike dry matter at anthesis, higher spike partitioning index and fruiting efficiency (grain set per unit of spike dry weight at anthesis), and the highest grain number per square meter (24.2 x 10(3) m(-2)). Simultaneously, HL maintained a higher leaf area index (LAI) at anthesis and a higher net photosynthesis rate (Pn) of flag leaves after anthesis, which contributed to a higher post-anthesis biomass; HL also had higher maturity biomass, harvest index (HI), and biomass remobilization in comparison to ML and LL. The above results demonstrated that HL improved grain yield by increasing grain number per square meter, post-anthesis biomass, biomass remobilization, maturity biomass, and HI. Additionally, HL also obtained higher NUtE by improving grain yield. Therefore, screening winter wheat varieties with traits such as HL can help achieve high and stable yields and high NUtE under rainfed conditions.