Fertilisers & Agrochemicals

World D — Polymers & Biomolecules

53.A — MACRONUTRIENTS & FERTILISERS

R53.01 The NPK Trio

Nitrogen (N): Promotes leaf/stem growth and green color (chlorophyll synthesis).
Phosphorus (P): Vital for root development, seed formation, and energy transfer (ATP).
Potassium (K): Enhances overall health, disease resistance, and water regulation.

R53.02 Nitrogenous Fertilisers

Most common: Urea ($NH_2CONH_2$). Contains ~46% Nitrogen.
Highly soluble in water. Synthesized using ammonia (from Haber Process) and $CO_2$.
Ammonium nitrate and ammonium sulfate are also widely used.

R53.03 Phosphatic Fertilisers

Derived from phosphate rock. Insoluble rock is treated with sulfuric acid to make it soluble.
Single Superphosphate (SSP): Mixture of calcium dihydrogen phosphate and gypsum.
Triple Superphosphate (TSP): Higher P content, no gypsum.

R53.04 Potassic Fertilisers

Muriate of Potash (KCl): The most common K fertiliser.
Sulfate of Potash ($K_2SO_4$): Used for crops sensitive to chloride (like tobacco).
Controls stomata opening/closing to manage water stress.

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R53.05 Insecticides

Chemicals that kill insect pests. Often act as nerve agents.
Organochlorines: DDT, BHC (Gammexane). Persistent in the environment (largely banned).
Organophosphates: Malathion. Degrade faster but are highly toxic to humans.

R53.06 Herbicides (Weedicides)

Target unwanted plants that compete with crops for nutrients/light.
2,4-D: A synthetic auxin. Causes broadleaf weeds to grow uncontrollably and die, while leaving grasses (like wheat) unharmed.
Glyphosate: Broad-spectrum weed killer.

R53.07 Fungicides

Prevent or eradicate fungal infections (mildews, blights, rusts).
Bordeaux Mixture: A classic mixture of Copper(II) sulfate and slaked lime. Widely used on vineyards.
Sulfur dusting is also a traditional fungicide.

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R53.08 Biomagnification

Many agrochemicals (like DDT) are fat-soluble and do not break down easily.
They accumulate in the fatty tissues of animals.
Concentration increases exponentially at each higher trophic level in the food chain.

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R53.09 Eutrophication

Runoff of excess N and P fertilisers into lakes and rivers.
Triggers explosive algal blooms that block sunlight.
When algae die, decomposing bacteria deplete the water's oxygen, suffocating aquatic life (Dead Zones).

R53.10 Biofertilisers

Living microorganisms used to enrich soil nutrients sustainably.
Rhizobium: Fixes atmospheric $N_2$ in the root nodules of legumes.
Mycorrhizae: Fungi that increase the root's surface area to absorb Phosphorus.

R53.11 Soil Amendments

Continuous use of chemical fertilisers can ruin soil pH.
Acidic Soil: Treated with slaked lime or crushed limestone (Calcium carbonate) to neutralize.
Alkaline Soil: Treated with Gypsum or organic matter.

R53.12 Integrated Pest Management (IPM)

A sustainable approach minimizing chemical pesticide use.
Relies on biological control (e.g., ladybugs eating aphids).
Uses crop rotation, pest-resistant GM crops, and pheromone traps to manage pest populations safely.