Balanced fertilization under different plant densities for winter oilseed rape (Brassica napus L.) grown on paddy soils in Southern China

[Display omitted] •Filed trials aimed to study oilseed rape response to fertilization and plant density.•Seed yield increased with increasing the levels of balanced N, P, K, S, and B.•Plant density had great effects on plant growth and little effects on seed yield.•Individual plant growth compensated seed yield under the low densities.•Chlorophyll and agronomic traits had great effects on seed productivity. Adequate amount of essential plant nutrients and plant density are vital factors influencing the productivity of oilseed rape (Brassica napus L.). Field experiments were conducted in southern China to study the influence of different fertilizing levels and planting densities on the seed yield, chlorophyll content and some growth traits of winter oilseed rape. Five fertilizing levels and six planting densities were set in a randomized block design. The tested planting densities were D1, D2, D3, D4, D5 and D6 with 7.5 × 104, 15 × 104, 22.5 × 104, 30 × 104, 37.5 × 104 and 45 × 104 plants ha−1, respectively. The tested fertilizing levels were F0 (control without fertilization), F1 (N = 60, P2O5 = 30, K2O = 52.5, S = 3.75, B =0.3 kg ha−1), F2 (N = 120, P2O5 = 60, K2O = 105, S = 7.50, B =0.60 kg ha−1), F3 (N = 180, P2O5 = 90, K2O = 157.5, S = 11.25, B =0.90 kg ha−1) and F4 (N = 240, P2O5 = 120, K2O = 210, S = 15, B =1.20 kg ha−1). The results showed that there were close relationships between the seed yield and fertilizing levels × planting densities. Below the fertilization level of F2, the seed yield increased as the planting density increased. Application of F3 caused a seed yield decline when the planting density surpassed 37.5 × 104 plants ha−1. The tested fertilizing levels caused remarkable increases in the seed yield but the plant density had little effects. The highest seed yield (2487 kg ha−1) was recorded in F4D3 followed by F4D1 (2308 kg ha−1), F4D5 (2303 kg ha−1) and F3D6 (2302 kg ha−1); while the minimum yield was obtained from the unfertilized soil treatments. The current research paper highlighted the importance of balanced N, P, K, S and B application under the different plant densities in winter oilseed rape. The individual growth of plants compensated the low plant density, but increasing the fertilization rates caused remarkable increases in the oilseed rape, suggesting that optimum nutrients rates are a critical factor in seed yield production.