Soybeans: Less nitrogen fertilizer used for planting

Soil requirements for soybeans are not strict, and the suitable pH is 6.5-7.5. It is intolerant to saline and alkaline, and high organic matter content can promote high soybean yield. Soybean root is a straight root system, root rhizobia and root "symbiotic nitrogen fixation" is an important source of nitrogen nutrition.

Soybeans require more fertilizer. Each production of 100kg soybeans 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 soil and fertilizers, and the other from the symbiotic nitrogen fixation of rhizobia, 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 root nodules decreases and the rate of nitrogen fixation decreases, which will increase the cost of soybean production. It is generally believed that early application of nitrogen can promote rapid seedling growth in areas where nitrogen deficiency is particularly present. Soybean seedling stage is the period of nitrogen construction. Applying a small amount of nitrogen fertilizer at seeding can promote the growth of seedlings.

Phosphorus has the effect of promoting the development of root nodules and can achieve the effect of "nitrogen addition by phosphorus". Phosphorus promotes root growth at the early stage of growth. Phosphorus promotes the growth of stem and leaf vegetative components before flowering. Phosphorus is abundantly supplied during flowering, which can shorten the process of genital organ formation. Phosphorus deficiency leads to a significant increase in flowering. Potassium can promote the growth of soybean seedlings, so that the stem is not strong lodging.

Applying lime on acidic soils not only supplies the necessary calcium nutrients for soybean growth, but also corrects the acidity of the soil. The effect of lime on increasing soil pH is often higher than that of increasing nutrients, making the soil environment conducive to rhizobia activity and increasing the effectiveness of other nutrient elements in the soil, such as molybdenum. In addition, calcium is very important in the initial stage of soybean nodule formation. Increased calcium in the soil can increase the number of soybean nodules. However, the application of lime can not be too much, generally not more than 450kg per hectare. The application of calcium superphosphate in production can meet the calcium requirement of soybeans.

The trace elements required for soybeans are iron, copper, manganese, zinc, boron, and molybdenum. On acidic soils, except for molybdenum, these elements are easily absorbed from the soil and are not lacking. Sometimes when the soil lacks molybdenum, it also becomes a limiting factor for production. However, molybdenum can accumulate in the soil. When there is too much molybdenum in the soil, it can also have a toxic effect on soybean growth.

The first deficiency of nitrogen in spring soybean is the yellowing of true leaves, which can be yellowed from the bottom up. There are parallel continuous or discontinuous iron patches along the leaf veins on the compound leaf. The chlorosis spreads from the tips of the leaves to the base, and the whole leaf is pale yellow. The veins of the leaves are also green; the leaves are small and thin, easy to fall off, and the stems are slender. Phosphorus deficiency nodule, slender stems, plant leaves dark green, thick leaves, uneven, long and narrow; phosphorus deficiency is severe, the veins yellow-brown, after the whole leaf was yellow. Deficiency of potassium leaf yellowing, symptoms from the lower position of the upper leaf development; leaf margin began to produce chlorotic spots, expand into pieces, plaques connected to the center of the leaf spread, and finally only the veins around the green. Yellow leaves are difficult to recover, leaves are thin, and they are easy to fall off.

The calcium deficient leaves yellow and brown spots, starting from the middle of the leaf and the tip of the leaf, the leaf margin veins are still green; the leaf margin is sagging, twisted, the leaves are small, narrow and long, and the tips of the leaves are tipped. The lack of molybdenum on the upper leaf color is light, the main and branch veins are lighter; there are contiguous yellow spots between the branch veins, the tip is easily green, and the later macular color is darkened to light brown; some leaves are uneven and twisted, and some main leaf veins appear in the center White line.

Soybeans use an organic-inorganic fertilizer application system and use phosphorus, nitrogen, potassium, calcium, and molybdenum as nutrient elements. Based on basal fertilizer, basal fertilizers are mainly organic fertilizers, and appropriate combinations of N, P, and K fertilizers are used. Generally, the amount of fertilizer applied to soybeans is nitrogen - 4 kg/mu, phosphorus 6 - 8 kg/mu, and potassium 3 - 8 kg/mu, including the sum of pure and effective nutrient contents of organic and inorganic fertilizers, and nitrogen includes the sum of base fertilizer and topdressing nitrogen.

( Jilin Provincial Academy of Agricultural Sciences Yan Xiaoyan)