Chapter 4 - Chemical fertilizers | Unit-II - Fertilizers and Soil Fertility Management | Notes - 5th Semester

Unit-II - Fertilizers and Soil Fertility Management

Syllabus

• Chemical fertilizers: classification, composition, & properties of major nitrogenous, phosphatic, potassic fertilizers, 
• Secondary & micronutrient fertilizers, Complex fertilizers, nano-fertilizers Soil amendments,
• Fertilizer Storage,
• Fertilizer Control Order.

Chapter 4 -

Chemical fertilizers

Chemical fertilizers are synthetic substances that contain essential plant nutrients such as nitrogen, phosphorus, and potassium. They are made by extracting these nutrients from natural resources such as rock phosphates, ammonia, and potash, and then processing them into concentrated forms that can be easily applied to crops. Chemical fertilizers provide a quick and easily accessible source of nutrients for plants, which can lead to rapid growth and increased yields.

However, excessive use of chemical fertilizers can have negative impacts on soil health and the environment. Overuse can cause soil compaction, salinity, and nutrient imbalances. It can also contribute to water pollution, as excess nutrients can leach into groundwater or run off into nearby water bodies, leading to harmful algal blooms and other environmental problems. It is important to use chemical fertilizers judiciously and in conjunction with other soil management practices to maintain soil fertility and environmental sustainability.

Classification

Chemical fertilizers can be classified based on their nutrient content and chemical composition. Here are some common types of chemical fertilizers:

1. Nitrogen fertilizers: These fertilizers contain nitrogen in various forms, such as ammonium nitrate, urea, and ammonium sulfate. Nitrogen is an essential nutrient that promotes plant growth and development.
2. Phosphorus fertilizers: These fertilizers contain phosphorus in various forms, such as monoammonium phosphate, diammonium phosphate, and triple superphosphate. Phosphorus is important for root development, flower formation, and fruit production.
3. Potassium fertilizers: These fertilizers contain potassium in various forms, such as potassium chloride and potassium sulfate. Potassium is important for plant growth and stress tolerance.
4. Compound fertilizers: These fertilizers contain a combination of nitrogen, phosphorus, and potassium in varying ratios, such as NPK 20-20-20 or NPK 10-30-10.
5. Secondary macronutrient fertilizers: These fertilizers contain calcium, magnesium, and sulfur, which are secondary macronutrients that plants need in smaller quantities.
6. Micronutrient fertilizers: These fertilizers contain trace elements such as iron, zinc, manganese, and copper, which are required in very small amounts by plants but are essential for their growth and development.
7. Controlled-release fertilizers: These fertilizers release nutrients gradually over time, providing a steady supply of nutrients to plants and reducing the risk of nutrient leaching.
8. Foliar fertilizers: These fertilizers are applied to the leaves of plants and provide nutrients directly to the plant tissue, bypassing the soil. They are often used as a supplement to traditional soil-applied fertilizers.

Chemical fertilizers can also be classified based on their solubility, granular or liquid form, and application method.

Composition, & properties of major nitrogenous fertilizers

There are several major nitrogenous fertilizers, each with their own unique chemical composition and properties. Here are some of the most commonly used nitrogenous fertilizers and their characteristics:

1. Urea: Urea is a white crystalline solid that contains 46% nitrogen by weight. It is the most commonly used nitrogen fertilizer worldwide because of its high nitrogen content and relatively low cost. Urea is highly soluble in water and can be applied to the soil or sprayed onto foliage as a foliar fertilizer. Urea is generally less volatile than other nitrogen fertilizers and has a low risk of causing nitrogen losses through ammonia volatilization.
2. Ammonium Nitrate: Ammonium nitrate is a white crystalline solid that contains 33% nitrogen by weight. It is a highly soluble fertilizer that can be applied to the soil or used as a foliar spray. Ammonium nitrate is highly volatile and can cause nitrogen losses through ammonia volatilization, especially under high temperatures and humid conditions. It is also a common ingredient in explosive mixtures, making it a potential security risk.
3. Ammonium Sulfate: Ammonium sulfate is a white crystalline solid that contains 21% nitrogen and 24% sulfur by weight. It is a soluble fertilizer that can be applied to the soil or used as a foliar spray. Ammonium sulfate is less volatile than ammonium nitrate, and has a lower risk of causing nitrogen losses through ammonia volatilization. It is also useful for acidifying alkaline soils due to its acidic nature.
4. Calcium Ammonium Nitrate: Calcium ammonium nitrate (CAN) is a granular fertilizer that contains 27% nitrogen by weight. It is a soluble fertilizer that can be applied to the soil or used as a foliar spray. CAN is less volatile than ammonium nitrate and has a lower risk of causing nitrogen losses through ammonia volatilization. It is also less hygroscopic than ammonium nitrate and is less likely to absorb moisture from the atmosphere.
5. Anhydrous Ammonia: Anhydrous ammonia is a gas that contains 82% nitrogen by weight. It is a highly concentrated nitrogen fertilizer that must be injected into the soil to prevent loss through volatilization. Anhydrous ammonia is extremely volatile and can cause severe burns if it comes into contact with skin or eyes. It requires specialized equipment and safety precautions for its handling and application.

In general, nitrogenous fertilizers provide a quick source of nitrogen to crops and help improve plant growth and yield. However, they can also have negative impacts on the environment if not used properly, such as causing eutrophication of water bodies and contributing to greenhouse gas emissions.

Composition, & properties of major phosphatic

There are several major phosphatic fertilizers, each with their own unique chemical composition and properties. Here are some of the most commonly used phosphatic fertilizers and their characteristics:

1. Superphosphate: Superphosphate is a granular fertilizer that is produced by reacting finely ground phosphate rock with sulfuric acid. It typically contains 16-20% P2O5 (phosphorus pentoxide) by weight. Superphosphate is a quick-acting fertilizer that provides a readily available source of phosphorus to plants. However, it is highly soluble and can be easily leached from the soil, making it less effective on sandy or heavily weathered soils.
2. Triple Superphosphate: Triple superphosphate is similar to superphosphate, but it is made by reacting phosphate rock with phosphoric acid instead of sulfuric acid. This results in a fertilizer with a higher phosphorus content of 46-48% P2O5 by weight. Triple superphosphate is also quick-acting, but it is less soluble and more stable in the soil than superphosphate.
3. Diammonium Phosphate: Diammonium phosphate (DAP) is a soluble fertilizer that is made by reacting phosphoric acid with anhydrous ammonia gas. It contains 18-46% P2O5 and 18-25% nitrogen by weight, depending on the grade. DAP is a popular fertilizer for crops such as maize and wheat, and it provides a readily available source of phosphorus and nitrogen to plants. However, it can be more expensive than other phosphatic fertilizers.
4. Monoammonium Phosphate: Monoammonium phosphate (MAP) is similar to DAP, but it contains a lower percentage of nitrogen (11-12%) and a higher percentage of phosphorus (48-61%) by weight. MAP is a soluble fertilizer that provides a quick-release source of phosphorus and nitrogen to plants. It is often used for high-value crops such as fruits and vegetables.
5. Rock Phosphate: Rock phosphate is a natural mineral that is mined from deposits of phosphorite rock. It typically contains 27-35% P2O5 by weight. Rock phosphate is a slow-acting fertilizer that must be finely ground before use to release its phosphorus content. It is often used as a source of phosphorus in organic farming and gardening, and it can improve soil fertility over the long term.

In general, phosphatic fertilizers provide a slow-release source of phosphorus to crops and help improve plant growth and yield. However, they can also have negative impacts on the environment if not used properly, such as causing eutrophication of water bodies and contributing to greenhouse gas emissions. Careful management and appropriate application rates are critical to minimize these negative impacts.

Composition, & properties of potassic fertilizers

Potassium (K) is an essential nutrient for plant growth and development, and potassic fertilizers are an important source of this nutrient. Here are some of the most commonly used potassic fertilizers, their chemical composition, and their properties:

1. Potassium Chloride (KCl): Potassium chloride is a water-soluble salt that contains 60-62% K2O (potassium oxide) by weight. It is the most widely used potassic fertilizer due to its relatively low cost and high solubility. Potassium chloride can be used on a variety of crops and soil types, but it can be harmful to plants in high concentrations.
2. Potassium Sulfate (K2SO4): Potassium sulfate is a water-soluble salt that contains 50-52% K2O and 17-18% sulfur (S) by weight. It is a good source of potassium for crops that are sensitive to chloride, such as tobacco and some fruits. Potassium sulfate is less soluble than potassium chloride, but it can be used in a variety of soil types.
3. Potassium Nitrate (KNO3): Potassium nitrate is a water-soluble salt that contains 44-46% K2O and 13-14% nitrogen (N) by weight. It is often used as a source of both potassium and nitrogen in greenhouse and hydroponic agriculture. Potassium nitrate is highly soluble and can be absorbed by plants quickly.
4. Langbeinite (K2Mg2(SO4)3): Langbeinite is a naturally occurring mineral that contains 22% K2O, 11% magnesium (Mg), and 22% sulfur by weight. It is a slow-release fertilizer that provides a long-lasting source of potassium and sulfur to crops. Langbeinite is less soluble than other potassic fertilizers, making it less prone to leaching.

In general, potassic fertilizers provide a readily available source of potassium to plants, promoting growth and increasing crop yields. However, excessive use of these fertilizers can lead to environmental problems such as soil salinization and nutrient imbalances. Careful management and appropriate application rates are critical to minimize these negative impacts.