Optimizing planting density to improve growth, yield and resource use efficiencies for winter oilseed rape under ridge-furrow film mulching

Ridge-furrow film mulching has been widely used as a water-saving and yield-increasing planting pattern in arid and semiarid regions. Planting density is also a vitally important factor influencing crop yield, and the optimal planting density will vary in different environments (such as ridge-furrow film mulching). How the combination of film mulching and planting density will affect the growth, physiology, yield, and water and radiation use efficiencies of winter oilseed rape is not clear yet. Therefore, a three-year field experiment was conducted from 2017 to 2020 to explore the responses of leaf chlorophyll (Chl) content, net photosynthetic rate (P_n), leaf area index (LAI), aboveground dry matter (ADM), root growth and distribution, yield, evapotranspiration (ET), water use efficiency (WUE), and radiation use efficiency (RUE) of winter oilseed rape to different film mulching patterns (F, ridge-furrow planting with plastic film mulching over the ridges; N, flat planting without mulching) and planting densities (LD, 100,000 plants ha^–1; MD, 150,000 plants ha^–1; HD, 200,000 plants ha^–1). The results showed that the F treatments led to significantly greater leaf Chl contents, P_n, LAI, and ADM, and a stronger root system than treatments without film mulching throughout the whole winter rapeseed growing seasons. Winter oilseed rape in the MD treatments had better physiological (leaf Chl contents and P_n) and growth (LAI, ADM, taproot, and lateral root) conditions than in LD and HD at the late growth period after stem-elongation. Grain yield in FMD was the greatest, and it was significantly greater by 34.8–46.0%, 6.7–9.6%, 87.8–108.3%, 38.7–50.3%, and 50.2–61.8% compared to those of FLD, FHD, NLD, NMD, and NHD, respectively. Furthermore, the ET in FMD was equivalent to FLD and FHD, but was markedly lower by 12.2–18.4%, 14.5–20.3%, and 14.6–20.4% than in NLD, NMD, and NHD. Finally, the WUE and RUE in FMD were significantly improved by 88.5–94.0% and 29.0–41.8% compared to NHD (the local conventional planting pattern and planting density for winter rapeseed). In summary, FMD is a favorable cultivation management strategy to save water, increase yield and improve resource utilization efficiencies in winter oilseed rape in Northwest China.