An improvement in oilseed rape (Brassica napus L.) productivity through optimization of rice-straw quantity and plant density

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.