Very low nutrient elements, there are six kinds of iron, copper, zinc, manganese, molybdenum, boron and so on. Trace element content in the crop body is small, but has a strong specificity, is the crop growth and development are indispensable and can not replace each other. Therefore, when the crop lacks any trace element, the growth and development are inhibited, resulting in reduced production and quality, serious or even no harvest. Conversely, if these elements are too many, poisoning will occur, affecting the yield and quality of crops, and may also cause the occurrence of certain endemic diseases in humans and livestock. Boron promotes the normal development of the reproductive organs. An important symptom of boron deficiency is that the seed cannot develop normally or even form, thus affecting the crop yield. Boron promotes the synthesis and transportation of sugar in crops. When boron is deficient, chloroplasts degrade and affect photosynthesis. Boron can increase the nitrogen-fixing activity of rhizobia and increase nitrogen fixation in leguminous crops. In the absence of boron, nodules are developed, affecting the amount of nitrogen fixed. Boron also enhances crop resistance. Molybdenum is a nitrogen-fixing microorganism, especially when rhizobia symbiotic with legumes fix atmospheric nitrogen. At the same time, it can increase the photosynthesis intensity of the leaves. In the absence of molybdenum, the plants were dwarf, their veins were chlorosis, and the leaf margins were charred and curled inwards, showing a wilting state. Zinc can promote the photosynthesis of crops, and the stagnation of crop growth and development occurs when zinc deficiency occurs. Plant chloroplast contains manganese and manganese can promote seed germination and seedling stage growth, and lack of manganese affects crop photosynthesis, respiration, and accumulation of nitrate nitrogen in the body. The phenomenon of chlorosis between leaf veins, brown spots, and gradually increased distribution in the whole leaf, so that the leaves become red-gray, leaf shrinkage. Iron is indispensable for the formation of chlorophyll and it is difficult to transfer in plants. Therefore, the leaf "chlormia deficiency" is the expression of iron deficiency in plants, and this chlorosis first appears on young leaves. In addition, iron affects the photosynthesis and respiration of plants. In the absence of copper, the growth of the plants was thin and the new leaves were yellow, withered and dry, and the tips of the leaves were curly white with necrotic spots.