The coupled effects of various irrigation schedules and split nitrogen fertilization modes on post-anthesis grain weight variation, yield, and grain quality of drip-irrigated winter wheat (Triticum aestivum L.) in the North China Plain

Irrigation methods and nitrogen (N) fertilization modes have complicated impacts on wheat physiology, growth, and development, leading to the regulation of wheat grain yield and quality. However, the optimal water-N combination for drip-irrigated winter wheat remains unclear. A two-year field study was conducted to evaluate the influences of various N-fertigation and water regimes on wheat post-anthesis grain weight variation, yield, grain NPK content, and grain quality. The two irrigation quotas were I₄₅ (irrigation when crop evapotranspiration reduced by effective rainfall (ETa-P) reaches 45 mm) and I₃₀ (irrigation when ETa-P reaches 30 mm), while the six N application rates were N_0–100 (100% at jointing/booting), N_25–75 (25% at sowing and 75% at jointing/booting), N_50–50 (50% at sowing and 50% at jointing/booting), N_75–25 (75% at sowing and 25% at jointing/booting), N_100–0 (100% at sowing), and SRF₁₀₀ (100% of slow-release fertilizer at sowing). The experimental findings showed that post-anthesis grain weight variation, grain yield, grain NPK content, and grain quality were all markedly influenced by the various irrigation schedules and N-fertilization modes. The N_50–50 treatment was more beneficial for winter wheat post-anthesis grain weight variation than the N_100–0 and N_0–100 treatments under the two irrigation quotas and during the two seasons. The highest grain yields of 9.72 and 9.94 (t ha⁻¹) were obtained with the I₄₅N_50–50 treatment in 2020–2021 and 2021–2022, respectively. The grain crude protein was higher in the I₄₅SRF₁₀₀ treatment during the two seasons. The I₄₅N_100–0 combination significantly (P<0.05) enhanced the content of grain total starch by 7.30 and 8.23% compared with the I₄₅N_0–100 and I₃₀N_0–100 treatments, respectively, during the 2021–2021 season. The I₄₅N_100–0 treatment significantly (P<0.05) enhanced the content of grain total starch concentration by 7.77, 7.62 and 7.88% compared with the I₄₅N_0–100, I₃₀N_0–100, and I₃₀N_25–75 treatments, respectively, in the 2021–2022 season. The principal component analysis (PCA) indicated that the N_50–50 split N-fertigation mode could be the optimal choice for farmers during winter wheat production via drip irrigation.