Unit 9a : ESSENTIAL PLANT NUTRIENTS

Form 1 Agriculture Lessons for JCE: Grow Your Knowledge

Essential plant nutrients are the chemical elements required by plants for optimal growth and development.

Essential plant nutrients are classified into two main groups based on the quantities plants require:

A. Macro Nutrients Macro-nutrients are those needed by plants in large quantities. They include:

Also included in this category, as they are required in large amounts and obtained primarily from air and water, are:

B. Micro Nutrients (Trace Elements) Micro-nutrients are those which are needed by plants in small quantities. They are:

Essential plant nutrients play crucial roles in various plant physiological processes:

They take part in enzymatic reactions, acting as cofactors for many enzymes.
They are structural components of the plant cell (e.g., cell walls, membranes).
They are constituents of cell metabolic compounds (e.g., chlorophyll, proteins, nucleic acids).
They are important in energy transformation reactions within the cell (e.g., photosynthesis, respiration).

Essential plant nutrients are depleted from the soil through various mechanisms:

Absorption by Plants and Crop Removal: As plants grow, they absorb nutrients from the soil. When crops are harvested and removed from the land, these absorbed nutrients are taken out of the soil system.
Volatilization: Some nutrients, particularly Nitrogen, can be lost to the atmosphere as gases (e.g., ammonia from urea, nitrogen gas ( $N_{2}$ ) through denitrification by bacteria).
Immobilization: Nutrients can be temporarily tied up by microorganisms as they build their bodies, making them unavailable for plant uptake.
Soil Erosion: Wind and water erosion carry away nutrient-rich topsoil, leading to significant nutrient loss.
Leaching: Soluble nutrients (especially nitrates and some sulphates) are washed vertically down the soil profile by water beyond the root zone, making them inaccessible to plants.
Fixation/Adsorption: Some nutrients (e.g., Phosphorus, Potassium, Iron, Manganese, Molybdenum) can react with soil components to form insoluble compounds or become tightly bound to soil particles (especially clay minerals), making them unavailable for plant uptake.

Essential plant nutrients can be supplied to the soil from various sources:

Decayed Organic Matter: The decomposition of plant and animal residues releases nutrients into the soil.
Organic Manure:
- Farmyard Manure (FYM): Decomposed animal waste mixed with bedding.
- Compost Manure: Decomposed organic materials (plant residues, food scraps).
Inorganic Fertilizers: Industrially produced chemical compounds containing specific nutrients (e.g., Calcium Ammonium Nitrate, Urea, Single Superphosphate).
Soil Amendments: Materials applied to improve soil properties, which may also add nutrients (e.g., lime application adds Calcium and Magnesium).
Rainwater: Rainwater can dissolve and carry some elements from the atmosphere to the soil.
Biochemical Nitrogen Fixation:
- Symbiotic Fixation: By Rhizobia bacteria in root nodules of leguminous plants.
- Non-symbiotic (Free-living) Fixation: By free-living bacteria like Azotobacter in the soil.
Atmospheric Nitrogen Fixation: Through natural processes like lightning, which converts atmospheric nitrogen into forms usable by plants.
Weathering of Minerals: Natural breakdown of rocks and minerals in the soil releases various nutrients.