6 Major Phosphate Fertilizers: MAP, DAP, MKP, MIKP, SSP, CMP

Phosphate fertilizers are mineral or synthetic compounds primarily supplying phosphorus (P) as an essential macronutrient for plant growth. There are five types of phosphorus fertilizers commonly used in crops, namely: monoammonium phosphate, diammonium phosphate, superphosphate, calcium magnesium phosphate fertilizer, and potassium dihydrogen phosphate.

I. Monoammonium Phosphate (MAP)

Chemical Formula: NH₄H₂PO₄
Key Properties:

• Acidity: pH 4-8 (soil-dependent), requires pH monitoring

• Solubility: 392 g/L at 20°C (rapid dissociation to H₂PO₄⁻ + NH₄⁺)

• Powder Common Nutrient Content:
  • N (ammoniacal nitrogen)-P₂O₅ (highly concentrated): 12-61-0
• Granular Common Nutrient Content:
  • N (ammoniacal nitrogen)-P₂O₅ (highly concentrated): 12-52-0 11-52-0 10-50-0 11-48-0 11-47-0 10-46-0 11-44-0

Comparison Between Thermal and Wet Processes for Monoammonium Phosphate (MAP) Production

1.1. Raw Material Pathways

1.2. Core Process Characteristics

Thermal Process Features:

• Reaction temperature: 1000-1200°C (P₄ combustion)

• Acid purity: ≥85% (impurities <0.5%)

• Neutralization: Gaseous NH₃ + thermal acid direct reaction

• Energy consumption: 8-10 tce/t MAP

Wet Process Features:

• Digestion temperature: 60-80°C

• Acid purity: 52-54% (1-3% impurities)

• Neutralization: Liquid-phase reaction requiring concentration

• Energy consumption: 3-4 tce/t MAP

1.3. Product Quality Comparison

Agronomic Applications:

• Crops: Cereals, oilseeds, horticultural plants

• Soil Compatibility: All types except high-pH calcareous soils

• Industrial Use: Base material for NPK compounds & water-soluble fertilizers (WSF)

II. Diammonium Phosphate (DAP)

Chemical Formula: (NH₄)₂HPO₄
Distinctive Characteristics:

• Alkalinity: pH 7.8-8.2 (neutralizes acidic soils)

• Powder Common Nutrient Content:
  • N (ammoniacal nitrogen)-P₂O₅ (highly concentrated): 21-53-0
• Granular Common Nutrient Content:
  • N (ammoniacal nitrogen)-P₂O₅ (highly concentrated): 18-46-0, 12-42-0

Application Guidelines:

• Optimal Soils: Acidic soils (pH <6.5)

• Restrictions: Avoid alkaline soils (pH >7.5) to prevent root scorching

• Regional Advisory: Not recommended for northern China’s calcareous soils

III. Single Superphosphate (SSP)

Composition: Ca(H₂PO₄)₂·H₂O + CaSO₄
Technical Specifications:

• Acidity: pH 2.5-3.5 (soil acidifying effect)

• P Availability: ≥12-18% P₂O₅ (highly soluble citrate-soluble P)

• Secondary Nutrients: ≥18-21% Ca, ≥8% S

Field Implementation:

• Target Soils: Acidic to neutral soils (pH 5.5-7.0)

• Precaution: Apply banded to minimize P fixation by Fe/Al oxides

• Soil Amendment: Enhances aggregate stability via gypsum content

IV. Calcium Magnesium Phosphate (CMP)

CMP is a natural mineral fertilizer produced by mixing phosphate rock with magnesium-silicon ores and calcining at temperatures above 1450°C to form a vitreous material, which is then water-quenched and ground. It undergoes no chemical treatment, contains no acid radicals, and has a pH of 8.5 (slightly alkaline), making it a natural conditioner for acidic soils and soils acidified by long-term chemical fertilizer use.

This fertilizer is rich in 10 macro, secondary, and micronutrients, including phosphorus (12%, 15%, or 18%), calcium (34%), magnesium (10%), and silicon (31%), as well as trace elements such as copper, iron, zinc, manganese, boron, and molybdenum. With total nutrient content exceeding 80%, it surpasses any compound fertilizer in nutritional value. Notably, its silicon content exceeds 31%, allowing it to also function as a standalone silicon fertilizer.

Chemical Structure: α-Ca₃(PO₄)₂ + CaMgSiO₄
Unique Attributes:

• pH Neutrality: 7.0-7.5 (no soil pH alteration)

• Nutrient Spectrum: powder or granular

  • P₂O₅: 16-18% 

  • CaO: 25-38%, MgO: 8-20%

• Mobility: Slow-release via silicate matrix

Deployment Strategies:

• Soil Types: Alkaline/sodic soils (pH >7.5)

• Synergistic Use: Combines with organic fertilizers to boost PUE by 25%

• Crop Suitability: Calcium-loving crops (e.g., tomatoes, apples)

V. Monopotassium Phosphate (MKP)

Formula: KH₂PO₄
Premium Features:

• P-K: 52% P₂O₅ + 34% K₂O

• Solubility: 220 g/L at 20°C (ideal for fertigation)

• pH Modulation: Buffers solution pH at 4.5-5.5

Precision Agriculture Applications:

• Crop Targets: High-value horticulture (e.g., grapes, greenhouse vegetables)

• Application Methods:

  • Base dressing: 200-400 kg/ha

  • Foliar spray: 0.3-0.5% solution

• PUE Enhancement: Reduces P fixation by 40% vs. conventional P sources

Ⅵ.Potassium Phosphite (MIKP)

• Chemical Formula: KH₂PO₃

• P-K: 58% P₂O₅ + 38% K₂O

• Systematic Name: Potassium dihydrogen phosphite

• Molecular Weight: 120.09 g/mol

• Phosphorus Oxidation State: +3 (phosphite form, PO₃³⁻)

• Appearance: White crystalline powder or granules

• Solubility: Highly water-soluble (≥600 g/L at 20°C)

• pH (1% solution): 6.0–6.5 (near-neutral)

Key Differences Between MKP (KH₂PO₄) and MIKP (KH₂PO₃)

1. Chemical Form

   • MKP: Orthophosphate (+5P, PO₄³⁻) – direct P nutrient.

   • MIKP: Phosphite (+3P, PO₃³⁻) – indirect P source + biostimulant.

2. Function

   • MKP: Pure P/K fertilizer (promotes growth/flowering).

   • MIKP: Dual role (P/K supply + systemic disease resistance).

3. Mobility

   • MKP: Xylem-mobile only.

   • MIKP: Phloem+Xylem mobile (faster translocation).

4. pH

   • MKP: Acidic (pH 4.5–5.5).

   • MIKP: Near-neutral (pH 6.0–6.5).

5. Usage

   • MKP: Base/top-dressing for yield.

   • MIKP: Foliar/drip for stress/disease prevention.

Note: MIKP is not a replacement for MKP but complements it in IPM programs. Avoid mixing MIKP with copper-based fungicides.

Agronomic Impact Summary

PUE: Phosphorus Use Efficiency

Conclusion: Toward Precision Phosphorus Management
The future of P fertilization lies in:

1. Product Engineering: Polymer-coated MAP for 60-70% PUE

2. Biological Integration: PSB-enhanced SSP formulations

3. Circular Systems: Urban P recovery for 30% supply substitution by 2030

“Optimizing phosphorus use isn’t merely agronomic efficiency – it’s existential necessity for planetary boundaries.”
― Global Phosphorus Initiative, White Paper 2024

Disclaimer: Nutrient availability data based on neutral citrate solubility (AOAC 958.01). Regional adaptations may apply.