way
1, natural nitrogen fixation
Scientists have found that some leguminous plants never need fertilization, but the content of soybean protein is very high. It turns out that there are many nodules on the roots of leguminous plants, and each nodule is a nitrogen fertilizer plant. At the same time, it is found that there are many rhizobia in the soil, which usually live on some decaying plants. When leguminous plants are planted in soil, rhizobia will drill into the cortex of leguminous plants along the tip of root hair and multiply in the cortex. Stimulated by the secretion of rhizobia, cortical cells also divide rapidly, forming small nodules around the central rhizobia. At this time, leguminous plants supply nodule with mineral elements, water and organic nutrients, while rhizobia use intracellular nitrogenase to reduce free nitrogen in the air into NH4+ nitrogen fertilizer for leguminous plants to use. Rhizobium is parasitic in leguminous plants, which contains nitrogenase, which can transform nitrogen in the air into nitrogen-containing compounds.
The function of nitrogenase can be simply described as follows: In addition to rhizobia of leguminous plants, there are nitrogen-fixing spirillus in the roots of Gramineae and other Gramineae crops, and some lower prokaryotic plants-nitrogen-fixing cyanobacteria and autotrophic nitrogen-fixing bacteria all contain nitrogenase, which has nitrogen-fixing effect. This category belongs to natural nitrogen fixation and biological nitrogen fixation. Lightning can convert nitrogen in the air into nitric oxide, and one lightning can produce 80 ~ 80~ 1500kg of nitric oxide. This is also a natural nitrogen fixation. Natural nitrogen fixation is far from meeting the needs of agricultural production.
2. Artificial nitrogen fixation
At the beginning of the 20th century, nitric acid and nitrogen fertilizer were produced by simulating lightning and electric arc. This kind of nitrogen fixation consumes a lot of electricity and costs a lot, so it was eliminated. This is an early artificial nitrogen fixation. Because the N≡N bond of N2 is very strong and the structure of nitrogen molecule is very stable, the chemical properties of nitrogen are inactive under normal circumstances.
Now, scientists in many countries in the world (including China) are studying simulated biological nitrogen fixation, that is, looking for artificial compounds with nitrogen fixation activity. Nitrogen-fixing enzyme consists of two kinds of protein. Protein (diazoenzyme) has a molecular weight of about 220,000 and contains two molybdenum atoms, 32 iron atoms and 32 active sulfur atoms. Another protein (diazoreductase) is composed of two identical subunits with a molecular weight of 29,000, and each subunit contains four iron atoms and four sulfur atoms. It has been found that some organometallic compounds can be used as soluble nitrogen fixation catalysts.
Because the N≡N bond of N2 is very strong and the structure of nitrogen molecule is very stable, the chemical properties of nitrogen are inactive under normal circumstances.