Question

How can the nutrient requirements of a plant be determined?

Answer 1

The chemical substances that are present in food and act as a raw material for body building and maintaining the functions of the body can be called as nutrients. Nutrients can be organic or inorganic in nature. Macromolecules such as carbohydrates, fats and proteins are organic in nature whereas $CO_{2}$, $H_{2}O$ and mineral ions are inorganic nutrients.

Complete answer:
- Plants also require several inorganic nutrients or minerals for their froth development, structure, physiology and reproduction.
- To determine the essential mineral nutrients, the method is solution culture technique. In this technique, plants are grown directly in a soil-free, defined mineral solution.
- This solution contains all the essential elements in proper proportion that are required for proper growth and development of plants. First, this technique was demonstrated by a prominent German.
- Botanist, Julius Von Sachs in 1860. He grew plants from seeds to maturity in a defined nutrient solution in absence of soil. This soil-less growth of plants in a nutrient solution is known as Hydroponics.
- In this process, plants are grown in a defined nutrient solution. This nutrient solution is prepared by mixing chemically pure mineral nutrient salts in purified water. The solution is taken in sterilised glass jars or polythene bottles covered with black paper.
- It minimises the risk of algal contamination and reaction of roots to sunlight. The jars are present with split covers or corks and have holes for suspending and holding seedling, a funnel for adding solution and a bent tube for aeration. Regular aeration of culture solution is essential for absolute growth and activities of roots.

Additional information:
Criteria for Essentiality: The criteria to determine the essentiality of an element include the following aspects.
1. The element must be absolutely necessary for supporting normal growth and reproduction of plants.
In the absence of the element, the plants do not complete their life cycle or set the seeds.
2. The element must be directly involved in the metabolism of the plant. It should form a component of either a structural or functional molecule.
3. The requirement of the element must be specific and not replaceable by another element.
4. Absence or reduced availability of the element causes disorders.
5. The disorders caused by absence or deficiency of an element can be corrected only by the availability of that element

Note: Many of the plants associate heavy and toxic minerals such as gold and selenium from the soil. While some plants growing near the nuclear test sites take up radioactive strontium. But, all the different types of mineral elements present in plants are not essential for plants. An element is said to be essential for plants if it has a specific structural or physiological role and without which plants cannot complete their life cycle. The criteria to know the essentiality of an element was proposed by Arnon and Stout in 1939.