How to balance fertilization for winter rapeseed during the Start of Winter?

(Agricultural Wealth Network) November 7 marks the Start of Winter solar term, and "Start of Winter" means the beginning of winter. Around the Start of Winter in most parts of China, precipitation decreases significantly, the air generally becomes drier, and the soil loses considerable water. Therefore, for regions growing winter wheat and winter rapeseed, preserving soil moisture and preventing drought is very important. The quality of soil moisture conditions is closely related to crop seedling growth and overwintering. A Jiangxi farming proverb says: "Start of Winter for rapeseed, Light Snow for wheat"; farming proverbs in various places also say, "Once Start of Winter arrives, plow the land, and you can increase the nutrients in the soil." Rapeseed is China's only winter oilseed crop, and it is also a good preceding crop that uses and improves the soil. Its root system is well developed and secretes large amounts of organic acids, which can decompose and utilize sparingly soluble phosphorus in the soil. China is a major producer of winter rapeseed, widely distributed across the provinces of the Yangtze River basin and the Yunnan-Guizhou Plateau. Scientific fertilization is an important part of achieving high yield, high quality and high efficiency in winter rapeseed. Rapeseed is a crop with high fertilizer demand, requiring more nitrogen, phosphorus and potassium than rice, and it is especially sensitive to phosphorus and boron. To produce every 100 kg of rapeseed, it needs to absorb 8-11 kg of nitrogen, 3-5 kg of phosphorus and 8.5-12.8 kg of potassium. When nitrogen is deficient, rapeseed plants are short, have few branches, and yield decreases. However, when nitrogen supply is excessive, it also causes increased protein in the seeds and decreased oil content; therefore, nitrogen fertilizer must be applied rationally. Only balanced fertilization can ensure that rapeseed yield and oil content remain at a relatively high level, while excessive nitrogen application causing an imbalance of nitrogen, phosphorus and potassium will significantly reduce the oil content of rapeseed. From the current production perspective, rational application of phosphorus, potassium and boron fertilizers can all increase rapeseed oil content and improve the fatty acid properties of the oil. Regarding the amounts and ratios of ingredients for balanced fertilization of rapeseed. On the premise of making full use of organic fertilizer, apply nitrogen, phosphorus and potassium fertilizers according to soil fertility level and yield target, mainly by controlling the amount of nitrogen fertilizer and increasing the application of phosphorus and potassium fertilizers. Taking the nutrient management recommendations for rapeseed production in Hubei Province as an example, the recommended amounts of nitrogen, phosphorus and potassium fertilizers are as follows: For a yield level above 200 kg/mu: recommended application of nitrogen fertilizer (pure N) 11-13 kg/mu, phosphorus fertilizer (pure P2O5) 4-6 kg/mu, potassium fertilizer (pure K2O) 7-9 kg/mu, borax 1.0 kg/mu; for a yield level of 100-200 kg/mu: nitrogen fertilizer (N) 8-10 kg/mu, phosphorus fertilizer (P2O5) 3-5 kg/mu, potassium fertilizer (K2O) 5-7 kg/mu, borax 0.75 kg/mu, etc. In terms of fertilization timing, because rapeseed has a long growth period, split application of nitrogen and potassium fertilizers can improve utilization efficiency. For this reason, appropriately increase the number of fertilizer applications; in addition to base fertilizer, also apply overwintering fertilizer, bud-bolting fertilizer and flowering fertilizer; for direct-seeded and relay-intercropped rapeseed, one additional seedling-promoting fertilizer is needed in winter. The split application of nitrogen and potassium fertilizers should appropriately reduce the amount used as base fertilizer and increase the proportion applied during the growth period. Specific fertilization timing: For transplanted rapeseed: 60% of the total nitrogen and potassium fertilizers is applied as base fertilizer, 20% as winter fertilizer (50 days after transplanting), and 20% as bolting fertilizer (80 days after transplanting); for direct-seeded rapeseed: 40% of the total nitrogen fertilizer is applied as base fertilizer, 30% as seedling-promoting fertilizer (about 25-30 days after sowing), 15% as winter fertilizer (about 80 days after sowing), and 15% as bolting fertilizer (about 110 days after sowing); 60% of the total potassium fertilizer is applied as base fertilizer, 30% as winter fertilizer (about 80 days after sowing), and 10% as bolting fertilizer (about 110 days after sowing), with the remaining fertilizer applied as base fertilizer. There is an important issue in current production: base fertilizer should be applied deeply to promote rapeseed root growth. Taking direct-seeded rapeseed as an example, it has an obvious taproot, and lateral roots are distributed along the taproot at various soil depths, and the lateral roots are not sufficiently developed. If fertilizer is applied only to the soil surface, it will lead rapeseed roots (including the taproot) to grow only in the surface soil rather than deeply, forming "floating roots," which causes unstable rooting of rapeseed, reduced ability to absorb soil water and nutrients, and easy occurrence of seedling lodging, fertilizer deficiency and drought stress. During the growth period of winter rapeseed, various natural disasters or harsh condition stresses are often encountered, such as the freezing snow disaster in early 2008, the drought in early 2009, and the unfavorable factors each year such as spring rain and wind during rapeseed flowering, as well as possible rainy weather at maturity, all of which are limiting factors for rapeseed production in China.