1. The nutrient elements needed for normal growth and development of plants are divided into essential elements and beneficial elements; Among the essential elements, there are many elements (also called constants) and trace elements.

2. Essential elements refer to plant nutrient elements that are necessary for the normal growth and development of plants and cannot be replaced by other elements. According to the needs of plants, essential elements are divided into essential macro elements and essential trace elements.

3. The essential macroelements are carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), sulfur (S), potassium (K), magnesium (Mg), calcium (Ca) and silicon (Si) (the latest plant physiology says that Si is a new macroelement).

4. The essential trace elements are iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (b), molybdenum (Mo), chlorine (Cl), sodium (Na) and nickel (Ni) (Na and Ni are new trace elements in the latest plant physiology).