When soybean is planted, nitrogen fertilizer is less used after flowering

Soybean has strict requirements on soil, suitable pH is 6.5-7.5, is not resistant to salt and alkali, and high organic matter content can promote high yield of soybean. Soybean root is a straight root system. Rhizobium and root have a "symbiotic nitrogen fixation" effect on the root, which is an important source of nitrogen nutrition.
Soybeans require more fertilizer, and each production of 100kg of soybean requires 8.30kg of nitrogen, 1.64kg of phosphorus and 3.72kg of potassium. Soybeans require a lot of nitrogen, one from the nitrogen contained in the soil and fertilizer, and the other from the symbiotic nitrogen fixation of Rhizobium, which can meet about 1/2 to 2/3 of the nitrogen required for high-yield soybeans. When excessive chemical nitrogen is applied, the number of nodules is reduced, and the rate of nitrogen fixation is lowered, which increases the cost of soybean production. It is generally believed that in areas where nitrogen is particularly deficient, early application of nitrogen can promote rapid growth of seedlings. Soybean seedling stage is a period of nitrogen requirement. Applying a small amount of nitrogen fertilizer during sowing can promote the growth of seedlings.
Phosphorus promotes the development of nodule and can achieve the effect of “phosphorus-increasing nitrogen”. Phosphorus mainly promotes root growth in the early growth stage, and phosphorus promotes the growth of vegetative bodies such as stems and leaves before flowering. Phosphorus supply during flowering can shorten the process of genital formation; phosphorus is insufficient, and the number of fallen flowers is significantly increased. Potassium can promote the growth of soybean seedlings, so that the stems are strong and do not fall.
Applying lime to acidic soils not only supplies the calcium nutrients necessary for soybean growth, but also corrects soil acidity. The effect of lime on increasing soil pH is often higher than increasing nutrients, making the soil environment conducive to Rhizobium activity and increasing the effectiveness of other nutrients in the soil, such as molybdenum. In addition, calcium is very important in the early stage of soybean nodule formation. An increase in calcium in the soil can increase the number of soybean nodules. However, the application of lime should not be excessive, generally not more than 450 kg per pen. The application of superphosphate on production can meet the demand for calcium in soybeans.
The trace elements required for soybeans are iron, copper, manganese, zinc, boron and molybdenum. In the acidic soil, except for molybdenum, these elements are easily absorbed from the soil and are not lacking. Sometimes when the soil lacks molybdenum, it will also become a production limiting factor. However, molybdenum can accumulate in the soil. When the amount of molybdenum in the soil is too high, it is also toxic to soybean growth.
The deficiency of nitrogen in spring soybeans is yellow in the true leaves, which can be yellowed from the bottom to the top. There are parallel continuous or discontinuous iron patches along the veins on the compound leaves. The chlorosis extends from the tip to the base, and the whole leaves are light yellow. The veins are also green; the leaves are small and thin, easy to fall off, and the stems are slender. The lack of phosphate root nodules, slender stems, the lower leaves of the plants are dark green, the leaves are thick, uneven, narrow and long; when the phosphorus deficiency is serious, the veins are yellowish brown, and the whole leaves are yellow. The potassium deficiency leaves are yellow, and the symptoms develop from the lower leaves to the upper leaves; the leaf edges begin to produce chlorotic spots, which expand into blocks, which are connected to the center of the leaves, and finally only green around the veins. Yellow leaves are difficult to recover, the leaves are thin and easy to fall off.
The calcium deficiency leaves are yellow and have brown dots. Starting from the middle of the leaves and the tip of the leaves, the leaf veins are still green; the leaves are drooping and twisted, the leaves are small, narrow and long, and the tip of the leaves is sharply fished. The surface of the molybdenum-deficient upper leaves is light, the main and branch veins are lighter; the membranous macular appears between the branches, the leaf tips are easy to lose green, and the yellow spots are darkened to light brown; some leaves are uneven and distorted, and some of the main veins appear in the center. White linear.
Soybean adopts organic and inorganic fertilizer application system, mainly phosphorus, nitrogen, potassium, calcium and molybdenum nutrients, based on base fertilizer, organic fertilizer is mainly used in base fertilizer, and appropriate application of chemical fertilizer nitrogen, phosphorus and potassium. Generally, the amount of soybean fertilization is nitrogen ~ 4kg / mu, phosphorus 6 ~ 8kg / mu, potassium 3 ~ 8kg / mu, including the sum of pure effective nutrient content of organic fertilizer and inorganic fertilizer, wherein nitrogen includes the sum of base fertilizer and topdressing nitrogen.
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