Abstract: To clarity the impacts of planting density and chemical regulation timing on the lodging resistance of soybean-maize intercropping system in Northern Xinjiang, we conducted a field experiment in 2023 in Xinyuan County, Ili, Xinjiang. There were three planting densities: 90000 and 150000 plants·hm^-2 for maize and soybean, respectively (low density, A₁), 105000 and 180000 plants·hm^-2(medium density, A₂), and 120000 and 210000 plants·hm^-2(high density, A₃) for maize and soybean, respectively. There were three chemical regulation treatments: water control (B₁), application of 30% amicarbinil·ethylene liming at seven-leaf stage (B₂), and nine-leaf stage (B₃) of maize. We measured the crop morphological properties, photosynthetically active radiation (PAR), lodging rate, carbohydrate content, and yield. Results showed that: 1) With the increases of planting density, plant height, ear height, and stem diameter of maize at silking stage decreased, while the height of soybean showed no significant change. Chemical regulation significantly optimized plant structure, with B₂ treatment showing the largest reduction. Compared with B₁, the height of maize and ear were reduced by 25.2% and 33.8%, respectively, and the height of soybean was decreased by 17.1%. Under dense planting conditions, earlier chemical regulation could optimize maize ear height coefficient. 2) Density increase reduced soybean canopy PAR and increased lodging rate. After chemical regulation, B₂ and B₃ treatments increased soybean canopy PAR by 12.2%-25.3% and decreased lodging rate by 57.7%-94.8% compared with B₁. 3) Density increase significantly reduced stem strength of maize and soybean, with reductions of 7.0%-15.9% for maize and 16.9%-29.9% for soybean when comparing A₂ and A₃ to A₁, respectively; structural (cellulose, lignin) and non-structural (soluble sugar) carbohydrate contents in maize stem decreased, while soybean non-structural carbohydrate content was highest in A₂. After chemical regulation, stem strength and carbohydrate content increased, with B₂ treatment showing the largest increase, indicating that chemical regulation could enhance crop mechanical strength and carbon assimilation capacity. 4) The crop yield increase was greater under B₃ treatment in A₁, and B₂ treatment in A₂ and A₃, with increases of 12.2%, 17.5%, and 25.9% compared with B₁, respectively. Under low density condition, chemical regu-lation treatment at nine-leaf stage improved yield by optimizing physiological metabolism and promoting the accumulation and distribution of photosynthetic products. Under medium and high density conditions, chemical regulation treatment at the seven-leaf stage achieved high yield by improving maize plant type structure (reducing plant height and ear height), increasing soybean canopy PAR, and simultaneously enhancing stem strength to significantly reduce lodging risk. In summary, the soybean-maize strip intercropping system in Northern Xinjiang performed the best under medium density and spraying 30% amicarbinil·ethylene liming at maize seven-leaf stage.

Key words: strip intercropping of soybean and maize, Northern Xinjiang, planting density, chemical regulation timing, lodging resistance characteristic