Mineral Nutrition in Plants
Dr. Riddhi Datta
Assistant Professor
Postgraduate Department of Botany
Barasat Government College
West Bengal
The Foundation of Global Food Production
Dr. Riddhi Datta
Environmental Costs of Fertilizer Use
While fertilizers are crucial for food production, their use carries significant environmental consequences
Energy Consumption
Over half of agricultural energy consumed by nitrogen fertilizer (production, distribution, application).
Resource Depletion
Phosphorus fertilizer production relies on nonrenewable resources, projected to peak this century.
Water Contamination
Fertilizer runoff causes widespread water contamination; many wells exceed safety standards.
Dr. Riddhi Datta
The Inefficiency Problem
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What Makes an Element Essential?
01
Required for Life Cycle
02
No Substitution Possible
03
Direct Involvement
Plants can synthesize all necessary compounds for normal growth if they have access to essential elements, water, and sunlight.
Dr. Riddhi Datta
Classification of Essential Elements
Macronutrients
Needed in large quantities
Micronutrients
Needed in trace amounts (ppm)
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Functional Classification: Four Essential Groups
1
Building Blocks
molecules.
2
Energy & Structure
3
Regulation
4
Electron Transfer
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Non-Essential but Beneficial Elements
Some elements, while not considered essential for all plants, can still accumulate in plant tissues and may even be beneficial. For example:
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Hydroponics: Growing Without Soil
Dr. Riddhi Datta
Dr. Riddhi Datta
Types of hydroponic systems
Standard Hydroponic System (Deep Water Culture): Plants are suspended with their stems just above a tank of nutrient solution. An air stone pumps air into the tank to fully saturate the solution with oxygen.
Substrate-based Systems: Plants are supported by inert materials like sand, gravel, or rockwool. The nutrient solution is flushed through this material. If the solution is delivered directly to the plant's base via a drip line, it is called a drip system.
Nutrient Film Technique (NFT): A pump circulates a thin, continuous layer of nutrient solution from a reservoir. The solution flows along a tilted channel, bathing the roots before returning to the reservoir, ensuring a constant supply of water and oxygen.
Dr. Riddhi Datta
Types of hydroponic systems
Aeroponics: Plant roots are suspended in the air and continuously sprayed with a nutrient solution. This method allows for easy control of the gaseous environment around the roots but requires a higher nutrient concentration and is not as widely used due to technical challenges.
Ebb-and-Flow Systems (Flood and Drain): Plant roots are periodically flooded with a nutrient solution, which then recedes, exposing the roots to a moist, oxygen-rich environment. Like aeroponics, these systems typically require a higher nutrient concentration.
Wick System: A simple, passive system that uses a wick to draw nutrient solution from a reservoir up into the growing medium where the plant's roots are located. It has no moving parts.
(E) Wick System
Nutrient Solutions: From Knop to Hoagland
1
1860s: Knop's Solution
Early formula with five mineral salts. Success was partly accidental—contaminated chemicals contained trace elements scientists didn't yet know plants needed.
2
1938: Hoagland's Medium
Dennis Hoagland at UC Berkeley created a precise mixture providing all known macro and micronutrients. Used tartaric acid to keep iron soluble.
3
Modern Modifications
Today's formulas use EDTA chelators for better iron availability, balanced nitrogen sources to stabilize pH, and optional elements like silicon for enhanced plant health.
Knop's Five Salts
Hoagland's Advancement
Dr. Riddhi Datta
Modern Nutrient Solution Essentials
High Concentrations
Solutions contain nutrient levels much higher than soil to ensure steady supply. Dilute for seedlings and young plants.
Balanced Nitrogen
Mix of ammonium (NH₄⁺) and nitrate (NO₃⁻) prevents pH swings and promotes healthy ion balance within the plant.
Chelated Iron
EDTA or DTPA molecules "cage" iron ions, keeping them dissolved and plant-available even in alkaline conditions.
What is a chelator?
A chelator is a molecule that binds to metal ions like iron, forming a stable, soluble complex. This prevents precipitation while allowing plant roots to absorb the nutrients. After absorption, the chelator releases back into solution to bind more ions—a continuous cycle that maintains nutrient availability.
Dr. Riddhi Datta
Diagnosing Nutrient Deficiencies
Element mobility determines where symptoms appear first—a crucial diagnostic tool
Mobile Elements
Nitrogen (N), phosphorus (P), potassium (K), and magnesium (Mg) can relocate from old to young leaves.
Symptom location: Older leaves show deficiency first
Immobile Elements
Calcium (Ca), iron (Fe), boron (B), and sulfur (S) cannot move from mature tissue to new growth.
Symptom location: Younger leaves and growing tips affected first
Remember: Multiple deficiencies can occur simultaneously, and symptoms may mimic viral diseases. In soil-grown plants, element interactions add complexity—hydroponics offers precise control for easier diagnosis.
Dr. Riddhi Datta
The Roles and Deficiency Symptoms of Essential Elements
An insufficient supply of an essential element leads to a nutritional disorder, resulting in specific deficiency symptoms.
Group 1: Elements that are Part of Carbon Compounds
This group includes nitrogen (N) and sulfur (S). They are essential for building core organic molecules like proteins and nucleic acids.
Nitrogen (N)
Role: Needed in greater quantities than any other mineral. It is a key component of chlorophyll, amino acids, and DNA.
Deficiency Symptoms: Stunted growth and chlorosis (yellowing), beginning in the older leaves. Severe deficiency can cause older leaves to turn tan and fall off.
Sulfur (S)
Role: A building block for amino acids and coenzymes.
Deficiency Symptoms: Similar to nitrogen deficiency—chlorosis, stunting, and purple coloration. However, because sulfur is less mobile, chlorosis typically appears in younger leaves first.
Dr. Riddhi Datta
The Roles and Deficiency Symptoms of Essential Elements
Group 2: Elements for Energy Storage and Structural Integrity
This group includes phosphorus (P), silicon (Si), and boron (B), which are often found in plants as ester linkages.
Phosphorus (P)
Role: A vital part of ATP, DNA, and cell membranes.
Deficiency Symptoms: Stunted growth, dark green leaves with dead spots, and sometimes a purple coloration due to excess pigment.
Silicon (Si)
Role: Reinforces cell walls, making plants more resistant to lodging (falling over) and fungal infections.
Boron (B)
Role: Critical for cell wall structure, cell elongation, and hormone regulation.
Deficiency Symptoms: Black necrosis of young leaves and terminal buds, with stems becoming brittle.
Dr. Riddhi Datta
The Roles and Deficiency Symptoms of Essential Elements
Group 3: Elements that Remain in Ionic Form
These elements, including potassium (K), calcium (Ca), and magnesium (Mg), are present as ions and are crucial for a variety of cellular processes.
Potassium (K)
Role: Regulates osmotic potential and activates many enzymes.
Deficiency Symptoms: Since it's mobile, symptoms start in older leaves as mottled or marginal chlorosis that turns into necrosis.
Calcium (Ca)
Role: Structural role in cell walls and acts as a signal for cellular processes.
Deficiency Symptoms: Immobile, so symptoms appear in younger leaves and meristematic regions, causing necrosis of root tips and young leaves.
Magnesium (Mg)
Role: The central atom in chlorophyll and required for enzyme activation.
Deficiency Symptoms: Mobile, so interveinal chlorosis (yellowing between the veins) first appears in older leaves.
Dr. Riddhi Datta
The Roles and Deficiency Symptoms of Essential Elements
Group 4: Elements Involved in Redox Reactions
This group consists of metals that can undergo reversible oxidation and reduction, making them essential for electron transfer reactions.
Iron (Fe)
Role: Component of electron transfer enzymes and crucial for chlorophyll synthesis.
Deficiency Symptoms: Immobile, causing interveinal chlorosis that starts in younger leaves. In severe cases, the entire leaf can turn white.
Manganese (Mn)
Role: Activates several enzymes and is essential for splitting water during photosynthesis.
Deficiency Symptoms: Interveinal chlorosis and small necrotic spots on the leaves.
Copper (Cu)
Role: Involved in redox reactions, especially in photosynthesis.
Deficiency Symptoms: Often results in dark green leaves with necrotic spots at the tips of younger leaves.
Nickel (Ni)
Role: Required by the enzyme urease.
Deficiency Symptoms: Buildup of urea and leaf tip necrosis.
Molybdenum (Mo)
Role: A component of enzymes for nitrogen fixation and nitrate reduction.
Deficiency Symptoms: General chlorosis and necrosis of older leaves. It can also cause "whiptail disease," where leaves are twisted and die.
Dr. Riddhi Datta