Maharashtra Board Class 11 Agriculture Science and Technology Chapter 6 Plant Nutrition PDF Download

Plant Nutrition

6.1 Essential Elements

6.1.1 Definition

The elements needed by the plant for their growth, development and completion of life cycle, without which plant will not be able to survive are called as essential elements.

Any living thing requires food (nutrition) for their growth, development and maintenance.

The food of plant is composed of certain chemical elements which are referred to as essential nutrients.

These elements are absorbed by plant roots principally as inorganic ions derived mostly form mineral constituents of the soil.

Depending upon the availability of the nutrients in soil, the nutrients content in a plant could be deficient, insufficient, sufficient, excess or toxic.

6.1.2 Criteria Of Essentiality

For an element to be regarded as an essential nutrient the following three criteria have been suggested by the scientist Arnon (1954).

The plant may be unable to grow normally or complete its life cycle in the absence of the element.

The element is specific and can not be replaced by any other element.

The element plays a direct role in the process of metabolism.

The following elements are recognized as essential (major) for plant growth. They are Carbon (C), Oxygen (O), Hydrogen (H), Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sulphur (S), Iron (Fe), Manganese (Mn), Zinc (Zn), Copper (Cu), Boron (B), Molybdenum (Mo) and Chlorine (Cl).

Now a days sodium (Na), Cobalt (Co), Silicon (Si) and some other elements are also being added to this list as supporting ones (minor).

Teacher's Note

Plants need many elements to grow well, just like we need different foods to stay healthy. For example, if soil does not have nitrogen, plants will become pale and weak like a sick child.

Exam Trick

Remember the three rules for essential elements: 1) Plant cannot grow without it, 2) No other element can replace it, 3) It does a real job in the plant. These three rules help you identify any essential element in exams.

Points To Remember

Plants need 16 important elements for growth.

Carbon, oxygen and hydrogen make 95 percent of plant weight.

Nitrogen, phosphorus and potassium are called primary nutrients.

Essential elements are absorbed by plant roots from soil water.

Each element has its own special job in the plant body.

6.1.3 Sources Of Elements

The deficiency symptoms of an element can be corrected by the application of that element.

Teacher's Note

Plants get nutrients from soil, water and air. For example, when farmers add NPK fertilizer to soil, plants can use nitrogen, phosphorus and potassium to grow big and strong.

Exam Trick

Remember: Air gives carbon and oxygen. Water gives hydrogen. Soil gives all other nutrients. This simple rule will help you answer any question about where nutrients come from.

Points To Remember

Carbon and oxygen come from air in the form of carbon dioxide.

Hydrogen comes from water in the soil.

Nitrogen comes from soil as nitrate or ammonium ions.

Phosphorus comes from rock phosphate mineral in soil.

All other nutrients are found in different rocks and minerals in the soil.

6.2 Classification Of Essential Elements

On the basis of quantity required by plants, the elements are classified as follows.

1. Major Or Macronutients

Major or macronutrients, are required by plants in large quantity. These include C, H, O, N, P, K, Ca, Mg and S. These are further subdivided as follows.

(a) Basic Nutrients - C, O, H

Carbon, oxygen and hydrogen constitute about 95% weight of plant. Field crops obtain most of their carbon and oxygen directly from the air. Hydrogen is derived either directly or indirectly from the soil water.

(b) Primary Nutrients -

Nitrogen, Phosphorus and Potassium are termed as primary nutrients as they are required in large amount by the plants. Their wide spread deficiencies can be corrected by the application of chemical fertilizers. Hence they are some times designated as 'fertilizer elements'.

(c) Secondary Nutrients -

Calcium, Magnesium and Sulphur are termed as secondary nutrients because they are required in moderate amount by the plants. Secondary nutrients are as significant as primary nutrients in plants but they are needed in moderate quantity.

Teacher's Note

Think of nutrients like food for plants. Just like you eat rice in large amount but salt in small amount, plants need nitrogen in large amount but sulphur in small amount.

Exam Trick

Easy way to remember: Basic nutrients = 3 (C, O, H). Primary nutrients = 3 (N, P, K). Secondary nutrients = 3 (Ca, Mg, S). All other 7 elements are micro nutrients.

Points To Remember

Macronutrients are needed in large amounts by plants.

Basic nutrients make 95 percent of plant weight.

Primary nutrients are N, P, K and they are in fertilizers.

Secondary nutrients are Ca, Mg, S and needed in moderate amount.

Micronutrients are needed in very small amounts.

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