Narrow Row Spacing Improves Yield of Delayed-Sown Winter Wheat by Enhancing Pre-Winter Tiller Quality

Delayed sowing frequently occurs in the North China Plain (NCP), restricting pre-winter population establishment and reducing grain yield. To determine whether narrow row spacing can alleviate yield loss under delayed sowing by improving the pre-winter stem and tiller basis, a randomized block experiment with two row spacings and four sowing-date regimes with adjusted planting density was conducted from 2021 to 2024. Yield components, pre-winter stem and tiller number and quality, and anatomical and physiological traits of the main-stem base and tiller nodes were measured. The results showed that 7.5 cm narrow row spacing (R2) increased tiller occurrence and improved hormonal balance and non-structural carbohydrate accumulation in the main-stem base and tiller nodes, and was associated with enhanced anatomical structural integrity and pre-winter stem and tiller quality. R2 increased final spike number, grain number per spike, thousand-grain weight, and grain yield by an average of 2.8%, 8.6%, 3.9%, and 10.7%, respectively, with the greatest yield increase under moderately delayed sowing (S2, 17.7%), and structural equation modeling (SEM) supported this possible yield-increasing pathway (χ2/df = 1.38, GFI = 0.90).These results provide a theoretical basis and technical reference for stabilizing and increasing yield in delayed-sown winter wheat in the NCP.