It was known that plant density and rice-straw returning affect the oilseed rape (Brassica napus L.) yield in oilseed-rice rotation system. But it was not clear if their interaction influences on oilseed yield and lodging resistance. Therefore our study aimed to study role of interaction between two plant densities (D1; 45 × 10⁴ plants ha⁻¹ and D2; 75 × 10⁴ plant ha⁻¹) and three levels of rice-straw returning (R1; 6 × 10³ kg ha⁻¹, R2; 9 × 10³ kg ha⁻¹ and R3, 12 × 10³ kg ha⁻¹) in improving seed yield and lodging resistance in oilseed-rice rotation system. Our results showed that the plant height and branch height increased, but the root crown diameter, branch number, pods per plant, yield per plant and lodging index decreased with the increase in plant density. Root crown diameter, branch height, pods per plant and lodging index increased while the plant height and seedling survival rate decreased due to increase in rice-straw returning. And the stem near the canopy was more prone to lodging. Low amount of rice-straw returning (R1) combined with low plant density (D1) can get high seed yield as the high seedling survival rate, while more rice-straw returning (R3) with higher plant density (D2) can elevate the seed yield by increasing the population pods and decreasing lodging index. Leaf area index (LAI), above ground nitrogen content and root nitrogen content decreased and the light transmittance (LT) increased at the bolting stage with the increase in plant density and rice-straw returning. However, the lower light transmittance (LT) associated with the increased pod area index (PAI) at the pod filling stage, which resulted in higher radiation use efficiency (RUE) and population biomass (PB). And in the pod filling stage, the above ground nitrogen content and root nitrogen content increased with the increase in rice-straw returning, but decreased with the increase in plant density, which resulted in the higher plant density and rice-straw returning, the higher nitrogen use efficiency (NUE). Besides, the activities of photosynthesis related enzymes fructose-1, 6-diphosphatase (FBP) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the lignin synthesis related enzymes phenylalanine ammonia-lyase (PAL) and peroxidase (POD) in stem increased at the flowering stage under high plant density and large amount of rice-straw returning, resulted in increasing lignin content and decreasing incidence of sclerotinia stem rot. Present study highlights that large amount of rice-straw returning with high plant density could be used as efficient agronomic practices to improve the productivity of oilseed rape under oilseed rape-rice rotation system.

已知植株密度和稻草还田会影响油菜-水稻轮作系统的油菜（Brassica napus L.）产量。但它们的相互作用是否影响油籽产量和抗倒伏性尚不清楚。因此，我们的研究旨在研究两种植物密度（D1；45 × 10 ⁴植物 ha ^-1和 D2；75 × 10 ⁴植物 ha ^-1）和稻草还田三个水平（R1；6 × 10 ³ kg ha ^-1 , R2; 9 × 10 ³ kg ha ^-1和 R3, 12 × 10 ³ kg ha ^-1) 提高油料-水稻轮作系统的种子产量和抗倒伏能力。结果表明，随着植株密度的增加，株高和分枝高度增加，但根冠直径、分枝数、单株荚数、单株产量和倒伏指数均呈下降趋势。由于稻草还田增加，根冠径、枝高、单株荚数和倒伏指数增加，株高和幼苗成活率下降。靠近树冠的茎更容易倒伏。低稻草还田量（R1）结合低植株密度（D1）可获得高产，幼苗成活率高，而稻草还田量（R3）高植株密度（D2）可提高种子产量通过增加种群数量和降低倒伏指数来增加产量。叶面积指数（LAI），随着植株密度的增加和稻草还田的增加，抽薹期地上氮含量和根系氮含量降低，透光率（LT）升高。然而，较低的透光率 (LT) 与豆荚填充阶段豆荚面积指数 (PAI) 的增加相关，从而导致更高的辐射利用效率 (RUE) 和种群生物量 (PB)。而在结荚期，地上氮含量和根系氮含量随着稻草还田的增加而增加，但随着植株密度的增加而下降，导致植株密度和稻草还田越高，氮利用效率（NUE）。此外，光合作用相关酶果糖-1、6-二磷酸酶（FBP）和核酮糖-1的活性，5-二磷酸羧化酶/加氧酶（Rubisco）和木质素合成相关酶苯丙氨酸解氨酶（PAL）和过氧化物酶（POD）在高植株密度和大量稻草还田下开花期增加，导致木质素含量和减少菌核病茎腐烂的发生率。目前的研究表明，在油菜-水稻轮作制度下，大量高密度稻草还田可作为提高油菜生产力的有效农艺措施。