Azotobacter provides nitrogen fixing bacteria which converts free nitrogen into nitrate and nitrites it increases soil fertility.

In the solution culture the plants are grown in pure nutrient media with only required elements. The glass containers are covered with black paper to protect roots from direct light. In other glass containers plant is allowed to grow artificially with same nutritive culture that contains all essential elements except one and its essentiality is to be judged. They are compared with the control plant grown in balanced nutrient medium. When there is any change in morphological features compared with normal plant this may be due to deficiency of specific element.

A) This is actively mobilized.
B) Highly mobile elements: Nitrogen and magnesium. Relatively immobile: Calcium and Boron.
C) The symptoms of deficiency of mobile elements are more pronounced in the older leaves and symptoms of deficiency of relatively immobile elements appear first in younger leaves. So this information can be utilized in horticulture as well as agriculture to get a broad idea of deficiency
elements in plants.

Plants require various minerals for their normal growth, development and metabolism.It means that all essential elements must be present in soil or in the air, water etc., wherever the plant grows.
Now, if any particular element or a group of element is supposed to be missing in the soil or in the atmosphere, the element will be deficient to that plant and the plant will eventually die of some or the other deficiency.

The technique of solution culture or hydroponic is the better technique to avoid contamination because in solution culture, the plants are grown directly in pure salt solution which are taken in suitable vessels(preferably made up of natural polyethene or borosilicate contamination.