Unit5 - Subjective Questions

Nitrogenous fertilizers are classified into four major groups based on the chemical form of nitrogen:

1. Ammoniacal Fertilizers: Nitrogen is present in the ammonium () form.

   • Examples: Ammonium Sulphate [], Ammonium Chloride ().
   • Properties: Readily soluble, resistant to leaching (adsorbed by soil colloids), acidic residual effect.

2. Nitrate Fertilizers: Nitrogen is present in the nitrate () form.

   • Examples: Sodium Nitrate (), Calcium Nitrate [].
   • Properties: Highly mobile, prone to leaching, basic residual effect, preferred by top dressing.

3. Ammoniacal-Nitrate Fertilizers: Contain nitrogen in both ammonium and nitrate forms.

   • Examples: Ammonium Nitrate (), Calcium Ammonium Nitrate (CAN).
   • Properties: Combined benefits of rapid availability () and retention ().

4. Amide Fertilizers: Nitrogen is present in amide () form.

   • Examples: Urea [], Calcium Cyanamide ().
   • Properties: Must undergo hydrolysis to ammoniacal form before plant uptake.

Composition and Properties:

• Formula:
• Nitrogen Content: 46% N (highest among solid straight N fertilizers).
• Physical State: White crystalline prills.
• Nature: Hygroscopic (absorbs moisture) and organic in nature.
• Residual Effect: Acidic.

Hydrolysis in Soil:
When applied to soil, urea undergoes hydrolysis in the presence of the enzyme urease (secreted by soil microorganisms) and water to form ammonium carbonate.

Ammonium carbonate is unstable and decomposes to release ammonium ions:

The ions can be absorbed by plants, fixed by clay minerals, or nitrified to nitrates.

Phosphatic fertilizers are classified into three groups based on their solubility:

1. Water-Soluble Phosphatic Fertilizers:

   • Phosphate is soluble in water and immediately available to plants.
   • Examples: Single Super Phosphate (SSP), Triple Super Phosphate (TSP), DAP.
   • Application: Suitable for neutral to alkaline soils and short-duration crops.

2. Citrate-Soluble Phosphatic Fertilizers:

   • Insoluble in water but soluble in 2% neutral ammonium citrate solution. Slowly available.
   • Examples: Dicalcium Phosphate (DCP), Basic Slag.
   • Application: Suitable for acidic soils and long-duration crops.

3. Insoluble Phosphatic Fertilizers:

   • Insoluble in water and citrate; soluble only in strong acids (e.g., mineral acids).
   • Examples: Rock Phosphate, Raw Bone Meal.
   • Application: Effective only in strongly acidic soils or for plantation crops where slow release is required.

Importance: This classification dictates the choice of fertilizer based on soil pH (e.g., Rock phosphate for acid soils vs. SSP for neutral soils) and the crop cycle length.

Comparison:

1. Muriate of Potash (MOP):

   • Chemical Name: Potassium Chloride ().
   • Nutrient Content: 60% .
   • Cost: Cheaper and widely used.
   • Disadvantage: Contains Chloride () ions which can be toxic to certain crops.

2. Sulphate of Potash (SOP):

   • Chemical Name: Potassium Sulphate ().
   • Nutrient Content: 50% and ~17.5% Sulphur.
   • Cost: More expensive.
   • Advantage: Chloride-free and provides Sulphur.

Conditions where SOP is preferred:

• Chloride-sensitive crops: Tobacco (affects burning quality), Potato (affects starch content), and Grapes.
• Sulphur-deficient soils: Since SOP provides secondary nutrient Sulphur.
• Saline soils: Application of MOP adds more chloride, aggravating salinity, whereas SOP has a lower salt index.

Definition:
Complex fertilizers are commercial fertilizers containing at least two or three of the primary plant nutrients (Nitrogen, Phosphorus, and Potassium) chemically combined in a single granule.

Examples:

1. Diammonium Phosphate (18-46-0)
2. Nitrophosphates (e.g., 20-20-0)
3. Ammonium Polyphosphate

Advantages over Straight Fertilizers:

• Balanced Nutrition: Supplies multiple nutrients simultaneously in a uniform ratio.
• Ease of Application: Requires less labor and time compared to mixing and applying individual straight fertilizers.
• Distribution: Granules are uniform in size and shape, ensuring even distribution of nutrients in the field.
• Storage: Usually usually non-hygroscopic and have better physical conditions, preventing caking.
• Cost-effective: Transport and handling costs are reduced due to high nutrient concentration per unit weight.

Definition:
Customised fertilizers are multi-nutrient carriers designed to contain macro and/or micro-nutrients, manufactured through a systematic process of granulation to satisfy the crop's nutritional needs, specific to its growth stage and the specific soil fertility status of a region.

Differences from Standard Complex Fertilizers:

• Specificity: Standard complex fertilizers have fixed grades (e.g., 10:26:26) applicable generally. Customised fertilizers are site-specific and crop-specific based on soil testing data.
• Micronutrients: Customised fertilizers often include micronutrients (Zn, B, Fe) tailored to local deficiencies, which standard complexes usually lack.
• Technology: They are produced using fusion technology to prevent segregation of nutrients, ensuring every granule contains the specific ratio of nutrients required for that specific region/crop.

Water Soluble Fertilizers (WSF):
These are fertilizers that are 100% soluble in water with very low impurity levels. They are primarily designed for application through irrigation systems (fertigation) or foliar sprays. They have high nutrient use efficiency (NUE) because nutrients are applied directly to the root zone in available forms.

Key Characteristics:

• Total solubility (no residue).
• Fast-acting.
• Low salt index to prevent burning during foliar application.
• Compatible with pesticides (in many cases).

Popular Grades:

1. 19:19:19 (N:P:K): A balanced starter grade for vegetative growth.
2. 13:0:45 (Potassium Nitrate): High potassium, used during fruiting/maturity stages.
3. 12:61:0 (Mono Ammonium Phosphate): High phosphorus, used for root development and flowering.

Concept:
Nano-fertilizers utilize nanoparticles (1–100 nm size) to deliver nutrients to plants. They can be synthesized by encapsulating nutrients within nanomaterials or by processing the nutrient itself into nanoscale particles.

Improving Nutrient Use Efficiency (NUE):

1. High Surface Area: The massive surface area-to-volume ratio increases the reactivity and metabolic absorption of nutrients.
2. Targeted Delivery: They can be engineered for slow release or targeted delivery, reducing losses via leaching (Nitrate) or volatilization (Ammonia).
3. Penetration: Nano-particles can easily penetrate plant stomata and cuticles when applied as foliar sprays, ensuring rapid uptake.
4. Reduced Quantity: Significantly lower quantities are required (e.g., 500 ml Nano Urea vs. 45 kg Urea bag) to achieve similar yields, reducing environmental load.
5. Controlled Release: They release nutrients in synchronization with crop demand, preventing nutrient fixation in the soil.

Definition:
Chelated fertilizers are micronutrients (like Fe, Zn, Cu, Mn) chemically bonded to an organic molecule called a 'chelating agent' (ligand), such as EDTA (Ethylenediaminetetraacetic acid) or DTPA.

Effectiveness over Inorganic Salts:

• Prevention of Fixation: In high pH (alkaline) soils, inorganic salts like Zinc Sulphate () react with hydroxide or carbonate ions to form insoluble precipitates (e.g., Zinc Hydroxide), becoming unavailable to plants.
• Protection: The ring structure of the chelate protects the metal ion from reacting with soil components.
• Mobility: Chelated nutrients remain soluble and mobile in the soil solution, allowing easier uptake by plant roots.
• Efficiency: Although more expensive per kg, the amount required is often less due to higher uptake efficiency compared to inorganic salts.

Given:

• Area = 2 ha
• Recommended Dose (RD): and

Step 1: Calculate Total Nutrient Requirement

• Total N needed =
• Total needed =

Step 2: Calculate Urea Requirement

• Urea contains (i.e., 46 kg N in 100 kg Urea).
• Formula:

Step 3: Calculate SSP Requirement

• SSP contains .

Result:
To fertilize 2 hectares, you need 521.74 kg of Urea and 750 kg of SSP.

Definition:
Soil amendments are substances added to the soil to improve its physical or chemical properties (specifically pH) to make it suitable for plant growth, rather than primarily to supply nutrients.

1. Amendments for Acidic Soils:

• Material: Liming materials like Calcite (), Dolomite [], or Quick Lime ().
• Function: Neutralize Hydrogen () and Aluminum () ions.
• Reaction:
  
  
  The ions are replaced by , raising the pH.

2. Amendments for Alkali (Sodic) Soils:

• Material: Gypsum (), Iron Pyrites ().
• Function: Replace exchangeable Sodium () with Calcium ().
• Reaction:
  
  
  Sodium sulphate () is soluble and must be leached out with water to reclaim the soil.

Fertilizer Grade:
The grade refers to the guaranteed minimum percentage of plant nutrients in the fertilizer, expressed as by weight. For example, the grade of Urea is 46-0-0.

Fertilizer Ratio:
This refers to the relative proportion of the three primary nutrients (N, P, and K) to each other in a fertilizer mixture or grade.

Calculation for 10:26:26:

• Grade: , , .
• To find the ratio, divide all numbers by the lowest non-zero nutrient content (10 in this case).
• Ratio
• Ratio = 1 : 2.6 : 2.6

This indicates that for every 1 part of Nitrogen, the fertilizer supplies 2.6 parts of Phosphorus and Potassium.

Storage of Fertilizers:

1. Moisture Protection: Fertilizers must be stored in dry, moisture-proof godowns with concrete floors and damp-proof courses. Hygroscopic fertilizers (like Urea, Ammonium Nitrate) absorb moisture rapidly.
2. Stacking: Bags should be stacked on wooden pallets (dunnage), not directly on the floor. Stacks should not exceed specific heights (e.g., 20 bags) to prevent pressure on lower bags.
3. Ventilation: Proper ventilation is needed, but doors/windows should be closed during humid weather.
4. Separation: Fertilizers should not be stored with pesticides or seeds to prevent cross-contamination.

Caking:
Caking is the formation of hard lumps in fertilizer bags due to moisture absorption followed by drying, or pressure from stacking. It makes application difficult.

Prevention of Caking:

• Coating: Coating granules with anti-caking agents (e.g., Neem oil for Urea, diatomaceous earth).
• Granulation: Producing uniform, hard granules reduces surface contact.
• Moisture-proof bags: Using HDPE/PP bags with liners.

Definition:
The Fertilizer Control Order (FCO) is a legal enactment by the Government of India issued under the Essential Commodities Act, 1955, to regulate the trade, price, quality, and distribution of fertilizers.

Primary Objectives:

1. Quality Control: To ensure that farmers receive fertilizers of the standard quality prescribed by the government.
2. Pricing: To regulate the maximum selling price of fertilizers to prevent overcharging.
3. Registration: To mandate the registration of fertilizer manufacturers, importers, and dealers.
4. Enforcement: To provide legal recourse and penalties for adulteration or black marketing.

Scope:
It specifies the physical and chemical standards (moisture, particle size, nutrient content) for all scheduled fertilizers sold in India. It defines sampling methods and laboratory analysis procedures.

Role of Gypsum ():

1. Reclamation of Sodic Soils: It supplies soluble Calcium () to replace exchangeable Sodium () on the clay complex. The displaced sodium is leached out as Sodium Sulphate.
2. Nutrient Source: It serves as a source of Calcium and Sulphur for crops (e.g., Groundnut).
3. Soil Structure: It helps flocculate soil particles, improving infiltration and aeration in dispersed sodic soils.

Gypsum Requirement (GR) Calculation:
GR is determined based on the Exchangeable Sodium Percentage (ESP) of the soil.

Where:

• = Current exchangeable sodium percentage.
• = Target ESP (usually 10-15%).
• = Cation Exchange Capacity (cmol/kg).

The theoretical value is multiplied by a factor (usually related to purity and efficiency) to get the actual field requirement.

Sources:

• Calcium (Ca): Gypsum, Single Super Phosphate (SSP), Lime (), Calcium Nitrate.
• Magnesium (Mg): Dolomite [], Magnesium Sulphate (Epsom salt), Magnesite.
• Sulphur (S): Elemental Sulphur, Gypsum ( S), SSP ( S), Ammonium Sulphate ( S).

Importance of Sulphur Fertilization:

1. Shift to High Analysis Fertilizers: The widespread shift from SSP (which contains S) to Urea and DAP (Sulphur-free) has induced S-deficiency in many soils.
2. Oilseed Production: Sulphur is crucial for oil synthesis. With the push for higher oilseed production (Mustard, Groundnut, Soybean), S demand has increased.
3. Intensive Cropping: Continuous mining of soil nutrients by high-yielding varieties without replenishment has depleted soil S reserves.
4. Quality: S improves protein content and quality in cereals and pulses.

Description:

• Composition: A mixture of Ammonium Nitrate () and Calcium Carbonate () or limestone.
• Nutrient Content: typically 25% Nitrogen (12.5% Ammoniacal + 12.5% Nitrate).
• Nature: Granular, grey or light brown.

Why 'Kisan Khad' (Farmer's Fertilizer)?

1. Neutral pH: Unlike Ammonium Sulphate (acidic) or Urea (acidic residual), CAN is neutral in reaction due to the presence of Calcium Carbonate. It does not alter soil pH, making it safe for repeated use.
2. Safety: Pure Ammonium Nitrate is explosive and hygroscopic. Mixing with limestone makes CAN non-explosive and improves handling properties.
3. Versatility: It is suitable for all crops and all soil types, hence very popular among farmers.

Definition:
Conversion factors are mathematical constants used to convert the elemental form of a nutrient (P, K) to its oxide form (, ) or vice versa. Fertilizer laws often require labelling in oxide forms, while scientific analysis uses elemental forms.

Phosphorus:

• From Element to Oxide:
• From Oxide to Element:

Potassium:

• From Element to Oxide:
• From Oxide to Element:

Derivation Logic: Based on atomic weights (P=31, O=16, K=39). E.g., molecular weight is 94, is 78. .

Concept:
Slow-release or Controlled-release fertilizers are designed to release nitrogen gradually over an extended period to match the physiological uptake requirements of the crop. This minimizes losses via leaching, volatilization, and denitrification, thereby increasing Nitrogen Use Efficiency (NUE).

Examples:

1. Coated Fertilizers: Sulphur Coated Urea (SCU), Neem Coated Urea (NCU), Polymer Coated Urea.
2. Chemical Condensation Products: Urea Formaldehyde (UF), Isobutylidene Diurea (IBDU).

Mechanism (e.g., Neem Coated Urea):

• Physical Barrier: The coating slows down the dissolution of urea in water.
• Nitrification Inhibition: Neem contains triterpenes (like Azadirachtin) which inhibit the activity of Nitrosomonas bacteria. This slows the conversion of Ammonium () to Nitrate (). Since Nitrate is the form most susceptible to leaching, slowing this process keeps nitrogen in the soil longer.