Humic Acid Fertilizer

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June 23, 2025, 10:43 AM

Guide

Highlights at a glance

This article provides a comprehensive overview of humic substances, focusing on their chemical and physical properties, sources, and quality standards. It details the classification of humic acids (HA), fulvic acids (FA), and humin based on molecular weight, solubility, and structural characteristics. HA are high-molecular-weight, aromatic-rich compounds soluble in alkaline conditions, while FA are smaller, more oxygenated, and water-soluble across all pH levels. Humin is the insoluble, highly stable fraction. Key functional groups include carboxyl, phenolic hydroxyl, and carbonyl groups, contributing to ion exchange and buffering capacity. The physical properties—such as color, solubility, pH (4–11), and electrical conductivity—are influenced by source and salt form (e.g., potassium/sodium humate). Sources include leonardite (high HA content, consistent quality), compost (variable composition, higher microbial activity), peat, and sapropel (rich in minerals). Quality varies by origin and processing, with international standards specifying minimum humic acid content (50–85%), low ash and moisture, and limits on heavy metals. Grades range from technical (50–65% HA) to super concentrate (>85% HA), supporting diverse agricultural applications.

1.Chemical and Physical Properties

1.1 Chemical Structure and Composition

1.1.1 Humic Substance Classification

Humic Acids (HA):
- Molecular weight: 50,000-100,000+ Daltons
- pH solubility: Soluble in alkaline conditions, precipitate in acidic pH
- Color: Dark brown to black
- Aromatic content: 30-45% of carbon structure
Fulvic Acids (FA):
- Molecular weight: 500-2,000 Daltons
- pH solubility: Soluble in all pH conditions
- Color: Light yellow to dark brown
- Higher oxygen content and lower molecular weight than humic acids
Humin:
- Molecular weight: >100,000 Daltons
- Insoluble in both acidic and alkaline conditions
- Most stable fraction of humic substances
- Forms soil organic matter matrix

1.1.2 Chemical Structure Characteristics

Aromatic Components:
- Benzene rings and phenolic structures
- Quinone and hydroquinone groups
- Lignin-derived aromatic compounds
- Condensed aromatic systems
Functional Groups:
- Carboxyl Groups (-COOH): 300-870 cmol/kg
- Phenolic Hydroxyl (-OH): 200-570 cmol/kg
- Alcoholic Hydroxyl: Variable content
- Amino Groups (-NH₂): Present in lower concentrations
- Carbonyl Groups (C=O): Ketone and aldehyde functionalities

1.1.3 Physical Properties

Appearance: Dark brown to black powder, granules, or liquid
Solubility:
- Water solubility varies with pH and source
- Potassium humate: 80-95% water soluble
- Sodium humate: 85-98% water soluble
- Free humic acid: 5-15% water soluble
pH:
- Solid humic products: pH 4-6 (acidic)
- Alkaline humate solutions: pH 8-11
- Buffering capacity: Strong pH buffering effect
Electrical Conductivity:
- Variable depending on salt content
- Potassium humate: 15-25 mS/cm at 1% solution
Moisture Content: 8-15% for solid products

1.2 Source Materials and Quality Variations

1.2.1 Leonardite-Derived Humic Acids

Source: Oxidized lignite coal deposits
Characteristics:
- High humic acid content (60-80%)
- Low ash content (5-15%)
- Consistent quality and composition
- Dark brown to black color
- Primary commercial source globally
Geographic Sources:
- North Dakota, USA (major source)
- Germany, Czech Republic, Russia
- China, India (emerging sources)

1.2.2 Compost-Derived Humic Substances

Sources:
- Municipal organic waste compost
- Agricultural residue compost
- Vermicompost (earthworm processed)
- Biosolids compost
Characteristics:
- Lower humic acid content (15-35%)
- Higher fulvic acid proportion
- Variable composition depending on feedstock
- Higher microbial activity
- Fresh organic matter components

1.2.3 Peat and Sapropel Sources

Peat-Derived Humic Acids:
- Source: Sphagnum and sedge peat deposits
- Characteristics: High fulvic acid content, acidic pH
- Geographic sources: Canada, Russia, Northern Europe
Sapropel-Derived:
- Source: Freshwater lake bottom sediments
- Characteristics: Balanced humic/fulvic ratio
- Additional minerals and trace elements

1.3 Quality Standards and Specifications

1.3.1 International Standards

Humic Acid Content:
- Minimum 50-80% (dry weight basis)
- Total humic substances: 60-85%
- Fulvic acid content: 15-25%
Physical Specifications:
- Moisture content:
- Ash content:
- Particle size: 80-200 mesh for powders
- Bulk density: 0.4-0.7 g/cm³
- Chemical Purity:
  1.3.2 Agricultural Grade Classifications