Foliar fertilizer is for the purpose of foliar absorption, and the nutrients needed by crops are directly applied to the foliar fertilizer, which is called foliar fertilizer. Foliar fertilizer is a type of fertilizer that nutrient elements are applied to the surface of crop leaves and are absorbed by the leaves. The leaves of plants have two layers of epidermis, which are composed of epidermal cells. The outer surface of the cells has a cuticle and wax. It can protect the mesophyll cells under the epidermal tissue to perform photosynthesis and respiration functions, and not be affected by changes in external adverse conditions. There are many tiny stomata on the leaf surface to perform the function of gas replacement. Studies have shown that the stratum corneum is composed of a long carbon chain fatty acid polymer with hydroxyl and carboxyl groups. The molecular gaps of this polymer and the hydroxyl and carboxyl hydrophilic groups on the molecule can allow the aqueous solution to penetrate into the leaf. Of course, The stomata on the surface of the leaf are more convenient channels for the leaf fertilizer to enter the leaf. Urea substances in fertilizers have a softening effect on the stratum corneum of epidermal cells and can accelerate the infiltration of other nutrients. Therefore, urea becomes an important component of foliar fertilizer.