bean cake is the residue after squeezing soybeans, and there are a lot of organic substances such as protein in it. After decomposition by biological fermentation, a large number of inorganic salts such as nitrogen fertilizer can be produced. Nitrogen fertilizer is one of the three major fertilizers needed for plant growth, which can make plants flourish and have dark green leaves. If you ferment, you can wet the bean cake, then pile it in a warm place with or without sunshine, then cover it with plastic film and seal it. Fermentation needs an anaerobic environment. As long as it is stable and suitable, it will be fermented in about half a month. It can be used as fertilizer when there is no smell. Remember to use it if it is not fermented, it will burn seedlings.