Study of Mineral Requirements on Plants: Do you know how plants obtain nutrition or how do they get energy for performing various activities? Any substance that is required by an organism to provide energy is known as a nutrient. Nutrition is the total of processes by which a living organism obtains raw materials for building the body and maintaining its function.

Mineral nutrition in plants is the study of the source, mode of absorption, distribution, and metabolism of various inorganic substances for plants’ growth, development, and reproduction. Read this article to know more about mineral requirements in plants, the classification and function of mineral elements, and different methods to study the mineral requirements in plants.

Methods to Study the Mineral Requirements of Plants

The mineral requirement of plants is determined by a solution culture experiment which was first developed by German scientist Julius von Sachs in 1860.

A normal or balanced solution for culture experiments is one having all essential elements in proper proportions is called a balanced nutrient solution.

The requirement of various inorganic raw materials for building the structure and maintaining the body functions of an organism is known as mineral nutrition. Various methods to study the mineral requirement of plants are:

1. Hydroponics: This is a technique of growing plants in a nutrient-rich environment
2. Aeroponics: This is a technique of growing plants in which roots are exposed in the air over a nutrient-rich medium.
3. Sand culture: In this technique, sand is used for growing plants and then nutrients are added into the medium.

Hydroponics

Solution culture is a technique in which plants are grown from seeds to maturity in a proper nutrient solution in the absence of soil. The growth of plants in this manner is known as hydroponics or soil-less growth. Hydroponics is used in the commercial production of many greenhouse crops.

Conditions required for the optimum growth of plants are:

(a) The concentration of mineral nutrients must be maintained at regular intervals.
(b) The solution must be properly aerated for the growth and activities of roots.
(c) The pH of the solution must be maintained at regular intervals of time.

Experiments are conducted in controlled environments to observe the growth of plants by nutrient film technique.

Nutrient film technique: The plants are grown in a tube having a thin film of recirculated nutrient solution. This solution is on a slight tilt so that it flows with the force of gravity. This system provides good aeration to not only the roots and nutrient uptake but also the pH and nutrient to be adjusted and monitored.

Fig: Nutrient film technique

There are various advantages as well as disadvantages of a hydroponic system. These are mentioned below:

Advantages of Hydroponics are:

1. It helps in obtaining a better yield of crops.
2. It helps in controlling soil-borne pathogens and helps in avoiding weeding problems.
3. This technique is helpful in water scarcity conditions.
4. Water can be conserved with this technique.
5. The pH of the crops can be regulated in the optimum range.

Disadvantages of Hydroponics are:

1. There occurs a need for continuous root aeration for the proper growth of plants.
2. The solution needs to be replaced at regular intervals for proper growth.
3. This is an expensive technique.
4. Some methods might spread water-borne diseases.
5. This technique cannot be used by traditional farmers due to a lack of knowledge.

Sand Cultures

In this type of culture, the plants are grown in the sand which is supplied with nutrient solution. Big vessels are used, which are filled with sand. Sand used here is washed with acid and distilled water. The nutrient solution is then added to the sand in regular intervals of time. The advantage of this technique is that the roots of plants are properly aerated.

Aeroponics

In this technique, roots are suspended in the air over the nutrient solution which is whipped into a nutrient mist by a motor-driven rotor. That means roots are supplied with moisture present in the air. Rooted plants are placed in a special box where the shoots of the rooted plants are exposed to air, and the roots are inside the box, having a controlled environment. The roots are sprayed with a nutrient solution for a short interval. A high level of oxygen available at the roots promotes the growth of microbes that digest the nutrient and makes them easily accessible to the plants. This is a recent method for the growth of plants. Plants that can be grown by this technique are citrus plants and olives.

Fig: Aeroponics

The difference between hydroponics and aeroponics are:

Hydroponics	Aeroponics
Hydroponics is a method of growing plants in a defined nutrient solution in the absence of soil.	Aeroponics is a method of growing plants where the roots are suspended in the air over the nutrient solution.
Roots of the plants are suspended in nutrient solution	The roots of the plants are exposed to the nutrient mist by a motor-driven rotor.
Water requirement is more in this system.	Water requirement is comparatively low in this type of system.
A medium is required for the growth of plants like soil.	Medium is not required in this type of system.
More variety of plants can be grown by this type of system.	Less variety of plants are grown in this type of systems such as olives and citrus plants
This is a cheap comparative cheap method.	This is a comparative expensive method.

Essential Mineral Elements

An essential element has a specific structural or physiological role in the activities of plants and without which plants cannot complete their life cycle.

Arnon and Stout, in 1939, proposed the criteria for determining the essential elements in plants. These criteria are:

1. The deficiency of these elements leads to disease in plants.
2. An element cannot be replaced by another element.
3. An element itself can correct the disorder caused by its deficiency.
4. These are necessary for the growth of plants.
5. The plant is unable to complete its vegetative and reproductive phase in the absence of these elements.

Based upon these criteria, there are 17 essential elements which are carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulfur, magnesium, calcium, iron, boron, manganese, zinc, copper, molybdenum, nickel, and chlorine.

Non-essential elements are also required by the plants in certain metabolic activities like cobalt, silicon, etc., but their deficiency does not cause disease to the plants.

Classification of essential mineral elements:
a) Based on the source from which they are derived

Based upon the source from which they are derived, essential elements are of two types, namely, mineral elements and non-mineral elements.
Mineral elements are the essential elements that are derived from soil, such as potassium, magnesium, etc.
Non-mineral elements are those elements that are derived from air or water, such as carbon, hydrogen, oxygen, and nitrogen.
b) Based on the amount required by the plants

Based upon the amount required by the plants, essential elements are classified as macroelements and microelements.
Macro-elements are those essential elements that are present in more quantities in plants. These elements are involved in the synthesis of organic molecules and help in the development of osmotic potential. There are nine macro-elements, namely, carbon, hydrogen, oxygen, nitrogen, potassium, phosphorus, sulfur, magnesium, and calcium.
Microelements are those essential which are present in less quantity in plants. These elements are involved in the functioning of enzymes as cofactors and activators. There are eight microelements, namely, iron, zinc, manganese, boron, copper, molybdenum, chlorine, and nickel.

Functions of Essential Elements

1. They are the constituents of biomolecules like nitrogen in amino acids, proteins, nucleic acid, etc.
2. They are the framework elements that constitute the cell wall like carbon, hydrogen, and oxygen.
3. These are the basic components of energy-related compounds like magnesium. Magnesium forms the component of chlorophyll, which helps in the photosynthesis process.
4. Some elements are toxic to the plants, like aluminum, mercury, etc. Some elements minimize the toxic effect of heavy elements like calcium, magnesium, etc.
5. These elements regulate the osmotic potential in plants. They are required for water absorption and maintenance of cell turgidity like sodium, potassium, etc.
6. Metals with variable valency act as electron carriers which helps in the oxidation-reduction system in plants like iron, copper, etc.
7. Certain mineral elements act as cofactors like magnesium is an activator of respiratory enzymes hexokinase, etc.
8. Certain elements take part in the opening and closing of stomata and other turgor movements like potassium.

Summary

Mineral nutrition in plants is the study of the source, mode of absorption, distribution, and metabolism of various inorganic substances for the growth and development of plants. The mineral requirement of plants was first determined by a solution culture experiment which was proposed by German scientist Julius von Sachs. An essential element has a specific structural or physiological role and without which plants cannot complete their life cycle.

There are various functions of essential elements like they are the basic components of biomolecules, they are required in energy-related compounds, they act as regulators in the oxidation-reduction system, etc. Various methods to study mineral requirements in plants are of three types, namely, hydroponics, sand culture, and aeroponics. Hydroponics is a technique of growing plants in a nutrient-rich medium in the absence of soil. Sand culture is a technique of growing plants in soil, and aeroponics is a technique of growing plants in which roots are exposed to the air.

Frequently asked questions (FAQs) on Study of Mineral Requirements of Plants

Q.1. What are essential elements?
Ans: An essential element has a specific structural or physiological role in the activities of plants and without which plants cannot complete their life cycle.

Q.2. Define hydroponics.
Ans: Solution culture is a technique in which plants are grown from seeds to maturity in a proper nutrient solution in the absence of soil. The growth of plants in this manner is known as hydroponics or soil-less growth.

Q.3. What are macro and micro-elements?
Ans: Macro-elements are those essential elements that are present in more quantities in plants. These are involved in the synthesis of organic molecules and help in the development of osmotic potential. Microelements are those essential which are present in less quantity in plants. These are involved in the functioning of enzymes as cofactors and activators.

Q.4. What are the functions of essential elements?
Ans: There are various functions of essential elements like they are the basic components of biomolecules, they are required in energy-related compounds, they act as regulators in the oxidation-reduction system, etc.

Q.5. Define aeroponics.
Ans: It refers to the type of hydroponic system in which roots are suspended in the air over the nutrient solution, which is whipped into a nutrient mist by a motor-driven rotor.

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