Unit 4: Fertilizers and Pesticides
Course Code: CHM-DSC-353
Paper Name: Industrial Chemistry
Table of Contents
1. Introduction to Fertilizers
Fertilizers are natural or synthetic substances containing chemical elements that improve the growth and productiveness of plants.
Essential Nutrients
- Primary Nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K).
- Secondary Nutrients: Calcium, Magnesium, and Sulphur.
- Micronutrients: Iron, Manganese, Boron, Zinc, etc.
NPK Value: A label on fertilizer bags (e.g., 10-20-10) indicating the percentage by weight of Nitrogen, Phosphorus (as P2O5), and Potassium (as K2O).
2. Nitrogenous Fertilizers: Urea
Nitrogen is essential for the synthesis of chlorophyll and proteins.
Manufacturing of Urea [NH2CONH2]
Urea is the most important nitrogenous fertilizer due to its high nitrogen content (~46.6%). It is produced by the reaction of liquid ammonia and liquid carbon dioxide at high pressure and temperature.
[Image of Urea production process flow diagram]- Reaction: 2NH3 + CO2 ⇌ NH2COONH4 (Ammonium Carbamate) → NH2CONH2 + H2O
- Forms: Usually sold as "Prills" or granules to prevent caking and facilitate easy spreading.
3. Phosphatic Fertilizers
Phosphorus is crucial for root development and energy transfer in plants.
- Single Superphosphate (SSP): Produced by reacting phosphate rock with Sulphuric acid. It contains 16-20% P2O5.
- Triple Superphosphate (TSP): Produced by reacting phosphate rock with Phosphoric acid. It is much more concentrated (~45-50% P2O5).
4. Pesticides: Classification
Pesticides are chemicals used to kill or control pests that damage crops.
| Category | Target Pest | Common Examples |
|---|---|---|
| Insecticides | Insects | DDT, BHC (Gammexane), Malathion |
| Herbicides | Weeds | 2,4-D, Atrazine |
| Fungicides | Fungi/Moulds | Bordeaux mixture, Organomercurials |
| Rodenticides | Rats/Rodents | Zinc Phosphide, Warfarin |
5. Environmental Impacts
While agro-chemicals increase food production, they pose significant environmental risks.
- Eutrophication: Runoff of nitrate and phosphate fertilizers into water bodies causes excessive algae growth, depleting oxygen and killing aquatic life.
- Bioaccumulation: Persistent pesticides (like DDT) accumulate in the fatty tissues of organisms and increase in concentration up the food chain (Biomagnification).
- Soil Degradation: Excessive use of chemical fertilizers can alter soil pH and kill beneficial soil microorganisms.
6. Exam Focus: Tips and FAQs
Exam Tips
- Urea Reaction: Memorize the two-step synthesis involving ammonium carbamate as an intermediate.
- Pesticide Safety: Mention the shift from organochlorines (DDT) to organophosphates (Malathion) because the latter are more biodegradable.
- Calculation: Be prepared to calculate the percentage of Nitrogen in Urea based on its molecular formula.
Frequently Asked Questions
Q: Why is DDT banned in many countries?
A: Because it is non-biodegradable, persists in the environment for decades, and causes reproductive failure in birds (thinning of eggshells).
Q: What is the composition of Bordeaux mixture?
A: It is a mixture of Copper Sulphate (CuSO4) and Slaked Lime [Ca(OH)2].
Q: What does the term "Bio-pesticide" mean?
A: These are pesticides derived from natural materials like animals, plants (e.g., Neem oil), and certain minerals.