Understanding Compound Fertilizers: Types, Manufacturing Methods, and Application Guidance

Fertilizers come in many types and can be classified into various categories:

• By chemical composition: Organic fertilizers, inorganic fertilizers, and organo-mineral fertilizers

• By nutrient content: Straight fertilizers, compound/blended fertilizers (multi-nutrient)

• By nutrient release speed: Fast-release fertilizers, slow/controlled-release fertilizers

• By physical state: Solid fertilizers, liquid fertilizers, gaseous fertilizers

• By chemical properties: Alkaline fertilizers, acidic fertilizers, neutral fertilizers

Among these, compound or blended fertilizers (multi-nutrient fertilizers) have been extensively introduced in our previous post, including their definitions, usage, advantages, and disadvantages. For a detailed review, please refer to the following link:🔗 https://www.kelewell.de/en/post/blended-fertilizer-compound-fertilizer-and-complex-fertilizer-understanding-the-differences

What is Compound Fertilizer?

Compound fertilizer refers to fertilizers containing two or more of the three essential nutrients: nitrogen (N), phosphorus (P), and potassium (K). These fertilizers offer high nutrient content, fewer secondary components, and favorable physical properties. They play a critical role in balanced fertilization, enhancing fertilizer use efficiency, and supporting stable and high crop yields.

As a major fertilizer category, compound fertilizers can be further subdivided based on nutrient composition, production process, functional characteristics, and crop specificity.

I. Mainstream Classification Methods

(1) By Nutrient Composition

1. Binary Compound Fertilizers

• N-P Type (e.g., Monoammonium Phosphate): Suitable for phosphorus-deficient soils or crops in phosphorus-demanding stages (e.g., rapeseed, potatoes).

• N-K Type (e.g., Potassium Nitrate): Ideal for leafy vegetables (e.g., spinach) or chlorine-sensitive crops (e.g., tobacco).

2. Ternary Compound Fertilizers

• Balanced Type: Versatile use throughout the entire growth cycle of field crops like wheat and rice (e.g., 15-15-15).

• High-N Type: Designed for vegetative growth in crops like maize and sugarcane (e.g., 30-5-5).

• High-K Type: Recommended for tuber crops (e.g., sweet potatoes), fruiting vegetables (e.g., tomatoes), and fruit trees during fruit enlargement (e.g., 15-15-20).

3. Multi-Nutrient Compound Fertilizers

• Fortified with secondary and micronutrients (e.g., calcium, magnesium). Best suited for cash crops like citrus and grapes or for improving poor soils.

(2) By Production Process

1. Tower Granulation Process

• Offers excellent water solubility (e.g., tower-based nitrate-sulfate compound fertilizers). Suitable for drip irrigation or crops requiring rapid nutrient uptake.

2. Press Granulation

• Slow-release characteristics make it suitable for sandy soils or low-input systems (e.g., eucalyptus plantations).

3. Bulk Blending (BB Fertilizer)

• Customizable formulas ideal for precision agriculture requiring flexible nutrient adjustments.

(3) By Potassium Source and Functional Properties

1. Chloride-Based Compound Fertilizers

• High-chlorine type (Cl >30%): Suitable only for chlorine-tolerant crops (e.g., rice, maize).

• Low-chlorine type (Cl 3%-15%): Use cautiously for chlorine-sensitive crops (e.g., tobacco, strawberries).

2. Sulfate-Based Compound Fertilizers

• Contain potassium sulfate; suitable for all cash crops (e.g., tea, watermelon), though more expensive.

3. Nitrate-Sulfate Compound Fertilizers

• Include nitrate nitrogen for rapid efficacy. Recommended for solanaceous crops (e.g., tomatoes) or early-stage topdressing.

4. Organo-Mineral Compound Fertilizers

• Include humic acid, improve saline-alkaline soils, and are ideal for organic farming or land with continuous cropping barriers.

(4) By Crop-Specific Applications

• Rice Fertilizer: Emphasizes high nitrogen + moderate phosphorus and potassium (e.g., 25-13-7).

• Fruit Tree Fertilizer: High potassium + trace elements (e.g., 15-5-25 + Zn).

• Leafy Vegetable Fertilizer: High-nitrogen type (e.g., 20-10-10).

• Chlorine-sensitive Crops (e.g., tobacco, grapes): Avoid chloride-based fertilizers; prioritize sulfate or nitrate-sulfate types. For mildly alkaline soils, acidic fertilizers such as MAP (monoammonium phosphate) are recommended. For cash crops, potassium humate-enhanced compound fertilizers are suggested to improve quality.

II. Mainstream Compound Fertilizer Production Processes

Compound fertilizer production can be broadly divided into three categories: chemical synthesis, physical mixing, and special granulation techniques. Each process affects the product's performance and application scenarios.

(1) Chemical Synthesis Methods

1. Tower Granulation

• Process: Urea/ammonium nitrate melt (135 °C) → mixed with phosphate and potash raw materials into slurry → sprayed from the top of a 45–125 m tower → cooled and solidified during free fall.

• Features: Uniform granules; contains biuret (up to ~1.5%); best for high-nitrogen formulas (phosphorus ≤15%).

• Example: Urea integration technology (e.g., twin-tower process using urea solution directly without crushing).

2. Ammoniation Granulation

• Involves reacting ammonia gas with phosphoric acid to form ammonium phosphate, then mixing with other materials. Nitrogen content can exceed 14%, with ≥95% water-soluble phosphorus.

(2) Physical Mixing Methods

1. Blending (BB Fertilizer)

• Direct mixing of straight N, P, and K fertilizers. Requires matching granule sizes (e.g., urea 2–4 mm, KCl screened >16 mesh). The coefficient of variation in nutrient uniformity should be <5%.

• Advantages: Formula flexibility (e.g., 20-15-10 corn fertilizer), equipment costs ~40% of tower systems.

2. Rotary Drum Granulation

• Uses physical tumbling for agglomeration. Simpler process but often results in uneven nutrient distribution, lower solubility, and higher nutrient loss.

(3) Special Granulation Techniques

1. Press Granulation

• Dry process forming granules under pressure (10–50 MPa); suitable for low-moisture raw materials (10–15%). Produces hard but slow-dissolving granules.

2. Spray Granulation

• Uses molten urea spray to form granules. Nitrogen content ~12%, water-soluble phosphorus ~80%. Mature technology but with lower nutrient use efficiency than ammoniation methods.

(4) Process Comparison and Application Scenarios

Process	Nutrient Uniformity	Typical Formulas	Recommended Applications
Tower	High	30-5-5 (High-N)	Topdressing, drip irrigation systems
Blending	Moderate	Customizable	Precision agriculture, sandy soils
Press	Low	Low-N, High-P&K	Slow-release needs, heavy clay soils

💡 Smart Fertilization Tips:

1. Soil testing and balanced fertilization: Know your soil and crop needs; avoid blind application.

2. Combine organic and inorganic fertilizers: Sustain productivity while improving soil health.

3. Base fertilizer as primary, topdressing as support: Apply most P & K and part of N as basal; split-apply fast-acting N according to crop stages.

4. Targeted micronutrient supplementation: Based on soil tests and crop sensitivity.

5. Utilize biofertilizers: Particularly valuable for continuous cropping, degraded soils, and reducing chemical fertilizer use.

6. Adopt proper application methods:

   • Deep application and soil covering: Reduce ammonia volatilization

   • Concentrated application: Improve phosphorus use efficiency

   • Foliar spraying: Rapid absorption and stress mitigation