What is the principle of nutrient absorption by crops?

There are three criteria for whether an element is the nutrient element needed by a plant during its growth.

①The lack of an element causes plant to be unable to complete the entire life cycle;

②The lack of an element will make the plant have strange symptoms in the process of growth,only if the element is added,these strange symptoms will disappear;

③This element has a direct nutritional effect on plant metabolism,but has no effect on growth environment.

Macro-elements include carbon,hydrogen,oxygen,nitrogen,phosphorus,and potassium,the content being several percent in plants

Medium elements include calcium, magnesium and sulfur.The contents of these elements are more in soil than in plants, so it is not necessary to supplement them by fertilization.

Trace elements include iron,copper,zinc,manganese,molybdenum,boron and chlorine,which are relatively few,but they are very important to plants.