The absorption of nitrogen, phosphorus, and potassium at different growth stages of soybean is consistent with the process of dry matter accumulation. The rate of nutrient absorption by young plants is slow, and after flowering, the plants begin to age and the rate of absorption decreases. Before the grains began to form, the plants had absorbed 60% of nitrogen, 55% of phosphorus and 60% of potassium. After the differentiation of flower buds of soybeans, molybdenum was absorbed from the soil, and molybdenum in the roots and pods of the pedicel stage was transferred to the grain and accumulated.
1. Seedling to branching. The important period for the formation of soybean vegetative organs is also the period when flower buds begin to differentiate. This period of lack of nitrogen, phosphorus, potassium, any element, not only the initial birth suppression, even if the normal nutritional conditions later, late fertility is not good. If there is enough phosphorus in the seedling soil, it can increase the number of flower bud differentiation. Based on the application of basal fertilizer, mainly seed fertilizer, re-apply phosphate fertilizer. The organic fertilizer has long-term fertilizer effect and is stable. It can not only meet the needs of soybean nutrient absorption from the seedling stage to the branching stage, but also meets the requirement of more fertilizer for late soybean growth. Applying inorganic nitrogen fertilizer directly in fertile soil has little effect on increasing yield. Even more nitrogenous fertilizer will inhibit the growth of soybean root nodules and reduce nitrogen fixation, which will reduce production.
2. Flowering period. Nitrogen, phosphorus, and potassium are required to grow rapidly. Two-thirds of the total nitrogen, phosphorus, and potassium are absorbed after the flowering period. In this period, nitrogen deficiency and calcium deficiency increased the rate of flower bud loss, and the grain yield was seriously affected. Nutrition analysis can be carried out by means of tissue analysis methods: the nitrogen content (above the dry weight) of the uppermost layer of the late flowering stage is 4.0% or less, and the excess is 7.0% or more; phosphorus content is less than 0.15%, and 0.8% or more. Excess; potassium content of 1.25% or less is lacking, and 2.75% or more is surplus.
3. Scarring to drum grain period. The key period for the formation of soybean production. The inorganic nitrogen absorbed by the roots, the nitrogen fixation of nodules, and the nitrogen stored in stems and leaves are all transported to the flower buds. In this period, if the supply of nitrogen, phosphorus and potassium were insufficient, grain production was seriously hindered. From the 10 days before the final flowering period to the next 3 to 4 weeks, it is the time when the fertilizer nitrogen and symbiotic fixed nitrogen are the most efficient in grain production. For every 1 gram of nitrogen uptake, the weight of the grain can be increased by 15 to 18 grams.
At this time, soybean nutrition mainly depends on the basal fertilizer applied at the early stage or the topdressing at the flowering stage. During the grain-granule period, especially at the end stage, nitrogen, phosphorus and potassium were transferred from the leaf and stem parts to the grain. The mature grain contained 68% of the total nitrogen absorbed, 73% of the total phosphorus, and 56% of the total potassium.
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