Nitrogen Fertilisation and Seed Rate Regulation Improved Photosynthesis, Grain Yield and Water Use Efficiency of Winter Wheat (Triticum aestivum L.) Under Ridge–Furrow Cropping

Ridge–furrow cropping patterns, nitrogen fertilisation and seed rate regulation are popular management strategies for improving crop yields in the semi-arid areas of Northwest China, but their interactive effects on grain yield and water use efficiency remain poorly understood. In 2020–2021 and 2021–2022, a two-season field experiment was conducted on winter wheat. There were two cropping patterns (C), ridge–furrow cropping with film mulch (RC) and traditional cropping without mulch (TC), two nitrogen fertilisation rates (N), 0 and 200 kg N ha⁻¹ (N₀ and N₁) and three seed rates (S), 240, 360 and 480 plants m⁻² (S₁, S₂ and S₃). The study was conducted in a split–split design with three replications (randomised blocks) and a total of 24 experimental plots. It was found that the interactive effects of C × N, C × S and N × S were significant on soil temperature (ST), leaf area index (LAI), relative chlorophyll content (SPAD), photosynthetic parameters, grain yield (GY) and water use efficiency (WUE) (p < 0.05), while C × N × S was significant only for LAI, aboveground biomass (AGB), GY and WUE (p < 0.05). Compared with TC and N₀, RC and N₁ significantly increased SPAD value (2.4% and 15.8%), net photosynthetic rate (P_n) (19.8% and 32.8%), net photosynthetic rate (P_n), transpiration rate (T_r) (7.0% and 15.7%) and the effective PSII quantum production (ΦPSII) (10.7% and 5.0%). The highest GY (6773 kg ha⁻¹ over 2020–2021 and 8036 kg ha⁻¹ over 2021–2022) and WUE (20.03 kg ha⁻¹ mm⁻¹ over 2020–2021, and 21.77 kg ha⁻¹ mm⁻¹ over 2021–2022) of winter wheat were observed under RC + N₁ + S₂. The findings showed that the RC cropping pattern with fertilisation and seed rate regulation (360 plants m⁻²) of winter wheat, which is appropriate for ensuring the long-term sustainability of agricultural production in the semi-arid regions of Northwest China, enhanced plant growth, photosynthetic traits, yield and water use efficiency. The study might give useful information for enhancing the productivity and water use efficiency of winter wheat in this and other similar climate locations.