Why the soybean root nodule is few and small?

There are nodules on the root of soybean, which can be used for symbiotic nitrogen fixation, which is an important source of nitrogen for legume crops. But in actual production, sometimes the root nodules of soybean are few and small, what is the cause of this?

Expert: when you encounter particularly serious symptoms, you should first think that it may be caused by the lack of trace element molybdenum. Because molybdenum is an essential trace element for nitrogen fixation in root nodules of legume crops, the absolute content of general crops is 1/1000000, while the molybdenum requirement of soybean is dozens of times higher than that of other crops. The main function of molybdenum is to promote the formation of soybean root nodules, increase the number of root nodules, and enhance the ability of nitrogen fixation of root nodules to enhance the ability of drought resistance.

The prevention and control measures of molybdenum deficiency in soybean are as follows:

First, mix seeds with molybdenum fertilizer. The commonly used molybdenum fertilizer is ammonium molybdate. When mixing seeds, use only 2 grams of ammonium molybdate per kilogram of bean seeds. First, dissolve ammonium molybdate in 5 times hot water, stir fully, cool and mix seeds. Second, molybdenum fertilizer was sprayed on the leaves before and after flowering. Ammonium molybdate solution with a concentration of 0.005% to 0.01% was sprayed. Foliar fertilizer spraying is usually sprayed more than twice. Third, because the symptoms of molybdenum deficiency often occur in acidic soil, the acidity of soil can be reduced and the availability of molybdenum can be improved by applying appropriate amount of lime. It should be noted that molybdenum fertilizer is mainly applied outside the root, generally without soil, in order to control the amount of molybdenum. Therefore, if the soil method is adopted, 200 grams of molybdenum fertilizer per mu should be fully mixed with organic fertilizer and then applied, not in the same field year after year. Fourth, before applying molybdenum fertilizer to soybean, it is necessary to find out whether the soil is deficient in phosphorus, and if it is deficient in phosphorus, it should be supplemented with phosphate fertilizer, otherwise the application of molybdenum fertilizer alone will reduce the number of nodules.

The nodule status of soybean is also related to the use of nitrogen fertilizer. If too much chemical nitrogen fertilizer was applied, it would also inhibit nodule nitrogen fixation, and also showed the decrease of nodule number, nodule size and nitrogen fixation rate of soybean.

In addition, phosphorus plays an important role in the growth and development of soybean nodules and nitrogen fixation. Phosphorus not only promotes root growth, but also contributes to the development of root nodules and improves the ability of nitrogen fixation. Therefore, in legume crops, we should pay attention to the application of phosphorus fertilizer, through the application of phosphorus fertilizer to promote nitrogen fixation, we can achieve the effect of "increasing nitrogen with phosphorus".