Ratio of nitrogen, phosphorus and potassium in soybean

Soybean in the seedling stage, appropriate edible nitrogen fertilizer to make the plant grow stronger, generally 7.5 to 10 kg urea per mu is appropriate. Spraying 0.2%~ 0.3% potassium dihydrogen phosphate solution or calcium superphosphate solution outside the roots at flowering stage can increase the nitrogen content of seeds and increase the yield obviously. Spraying 0.1% borax, copper sulfate and manganese sulfate solution at flowering stage can promote the fullness of seeds and increase the oil content of soybean.

I. Nutrient requirements of soybeans

Soybean has relatively high economic value among grain and oil crops. Although soybean needs a lot of nitrogen, it can be fixed by nodules. Generally, 5-7.5 kg/mu can be obtained from the atmosphere, which is about 40%-60% of the nitrogen required by soybean. For every 100 kg of soybeans produced, 1.8-10.1 kg of nitrogen, 1.8-3 kg of phosphorus and 2.9-3 kg of potassium are absorbed from the soil. Soybean absorbs much more nutrients than rice, wheat and corn.

2. The law of soybean fertilizer absorption

Soybean growth and development can be divided into seedling stage, branching stage, flowering stage, pod setting stage, seed filling stage and mature stage. The whole growth period is 90-130 days, and the law of fertilizer absorption is nitrogen absorption rate. 15% of total nitrogen uptake was in seedling and branching stages, 16.4% in branching to full bloom, 28.3% in full bloom to pod setting, and 24% in puffing stage. The peak period of nitrogen uptake was from flowering to seed filling. Phosphorus uptake rate. 17% from seedling stage to early flowering stage, 70% from early flowering stage to puffing stage, 13% from puffing stage to mature stage. The phosphorus requirement of soybean was the highest in the middle growth period. Potassium uptake rate. 43% of potassium was absorbed before flowering, 39.5% from flowering to grain filling, and 17.2% from grain filling to maturity. Therefore, the period from flowering to seed filling is not only the peak period of dry matter accumulation, but also the peak period of N, P and K uptake.

3. Key points of soybean fertilization technology

Fertilization system of soybean generally consists of basal fertilizer, seed fertilizer and topdressing. The principle of fertilization is to ensure that soybean has sufficient nutrition, but also to play the role of rhizobia nitrogen fixation. Therefore, no matter in the early or late growth, nitrogen should not be excessive, so as not to affect the growth of rhizobia or cause lodging.

But on the other hand, the misconception that "soybean has rhizobia and does not need nitrogen" must also be corrected. Fertilization should be carried out to achieve a reasonable combination of nitrogen, phosphorus, potassium and trace elements such as boron and molybdenum, and use both delayed and available fertilizers.

Soybean fertilization needs to master the law, so that soybeans can grow better, soybean oil content is higher, profits are higher.