Rapeseed is a phosphorus-loving crop. Its phosphorus requirement is more than twice that of cereal crops, and it is sensitive to phosphorus. Rapeseed with mild phosphorus deficiency grew slowly. Although it could bolt and blossom, it had fewer branches, fewer horns, unsaturated grains and more blighted grains. Under severe phosphorus deficiency, the root system grows poorly, the leaves become smaller, the mesophyll becomes thicker, the middle and lower leaves are not lustrous, the leaves are dark purple, the veins are purple red, the upper leaves are dark green and gray, the leaves are wrinkled and erect, and can not spread, some plants will gradually wither and die. According to the experiment, the rapeseed yield was increased by 0.9 kg of superphosphate, 1.2 kg of rapeseed per kg of calcium magnesium phosphate, and 0.4-0.6 kg of rapeseed per kg of phosphate rock powder.
Although P uptake by rapeseed was the highest at bolting stage, P application at seedling stage was the best in terms of utilization rate and yield increasing effect of P fertilizer. The results showed that the utilization rate of phosphorus before 2-leaf stage was 17.3%, while that before bolting stage was 8.5%. The yield of rape was only 27.4% of that before 2-leaf stage. Because phosphorus can be reused in rapeseed, the earlier the absorption period is, the higher the efficiency is. Early application of phosphorus fertilizer can increase the concentration of plant cell fluid, enhance cold resistance and resist freezing injury, so as to ensure the safe overwintering of rapeseed. It can also promote the early growth period and increase oil content by 0.5% - 2.4%.
Therefore, phosphorus fertilizer should be applied early, and it is better to be used as base fertilizer of Seedbed and fixed root fertilizer when planting or transplanting. If it is too late to apply phosphorus in sowing, it should be applied before the 5th leaf stage, the earlier the effect is, the better. The amount of phosphorus fertilizer is generally 20-25 kg per mu of superphosphate or calcium magnesium phosphate fertilizer. If the soil is seriously deficient in phosphorus or the soil with high amount of nitrogen fertilizer, it should be applied more appropriately. Rapeseed roots have special phosphorus uptake capacity. Phosphorus fertilizer, which is difficult to use in general crops, has good fertilizer effect on rapeseed. Therefore, when rapeseed is planted on acid soil, it can be applied with phosphorus rock powder as a kind of late-acting phosphorus fertilizer.