N- is a constituent element of protein, nucleic acids (DNA and RNA) and chlorophyll in chloroplasts in plants, which plays a great role in the growth and development of plants. P- is an element of nucleic acids (DNA and RNA), protein and enzymes in plants, which promotes plant growth and enhances the cold and drought resistance of crops. Potassium can promote photosynthesis and use the osmotic pressure of cells to absorb water. Enhance the tolerance of plants to various adverse conditions. Lack of N inhibits plant growth, and plants are short, short and loose. Potassium deficiency can also inhibit plant growth. Plants will bend branches, stems will grow abnormally, and plants will be in a lodging state. Phosphorus deficiency will weaken the resistance of plants to harsh environment. Plants can't resist cold and heat. You can remember that "potassium resists lodging, phosphorus resists drought (cold), and nitrogen fertilizer is used to loosen branches and leaves."