Abstract: Culm lodging is a common problem in wheat (Triticum aestivum L.) production causing yield loss and quality deterioration of grain. Weak mechanical strength of the 1^st and 2^nd basal internodes of culm is the major reason for wheat lodging during late growth period. It is well known that the mechanical strength is closely related to cellulose and lignin contents in culm, which are easily affected by nitrogen fertilizer. Accordingly, lodging resistance can be improved through proper nitrogen application. However, few reports have been found on it so far. We attempted to set up a nitrogen application regime for increasing longing resistance in high-yielding winter wheat through measuring the structure parameters of culm, chemical components of culm cell walls, and the culm lodging resistance index (CLRI). In the present experiment, we employed a wheat cultivar “Yannong 19” with high yield and strong-gluten content in the field with basic nutrition status in 0–20 cm soil layer as organic matter of 2.13%, total N of 1.5 g kg^-1, available N of 115.6 mg kg^-1, available P of 22.8 mg kg^-1, and available K of 142.5 mg kg^-1. N fertilizer treat-ments were set up by randomized block design with three application rates (202.5, 270.0, and 337.5 kg ha^-1, respectively) and three basal-topdressing ratios at pre-sowing, jointing, and booting stages (3:5:2, 5:5:0, and 7:3:0, respectively). The planting den-sity was 2.25´106 plants ha^-1. The results showed that N fertilizer application model significantly affected lodging-resistant capa-bility. Lengths of the 1st and 2nd basal internodes and their N contents increased with the increase of nitrogen levels, especially the basal nitrogen proportion. The cell wall cellulose and lignin contents, and culm lodging resistance index showed the trend of low-high-low in the 3 N levels, but kept decreasing when more basal nitrogen was applied. CLRI was positively correlated with the diameter of basal internodes (r = 0.9254**), thickness of culm wall (r = 0.9087**), filling degree (r = 0.9218**) and mechanical strength (r=0.9662**) of culm, but negatively correlated with the length (r = -0.8421**) and the nitrogen content (r = -0.8658**). The study also indicated the potential of CLRI for wheat lodging evaluation.

Key words: Winter wheat, Nitrogen application model, Lodging resistance, Culm lodging-resistance index(CLRI)