Humic acid is not a fertilizer in the usual sense: it is a soil conditioner made from decomposed organic matter. It supplies little nitrogen, phosphate or potash on its own. Growers use it to help soils hold nutrients and water and to improve how crops respond to the fertilizer they already apply.
What humic and fulvic acids are
Humic substances form when plant and animal material decomposes over long periods. They are grouped by how they dissolve:
| Fraction | Solubility | Molecule size |
|---|---|---|
| Humic acid | Dissolves in alkaline solutions, not in acid | Larger |
| Fulvic acid | Dissolves at any pH | Smaller |
| Humin | Does not dissolve | Largest |
Where commercial humic products come from
- Leonardite: an oxidised form of lignite, and the most common raw material for concentrated humic products.
- Lignite and brown coal.
- Peat.
- Compost and other organic residues.
The raw material is usually extracted with an alkali, most often potassium hydroxide, to make soluble potassium humate. That is why many humic products also contain some potassium.
What humic acid does in the soil
Research and field experience point to several effects, although results vary a great deal with soil, crop, product and rate:
- Holds nutrients: humic substances add to the soil’s cation exchange capacity, helping it retain potassium, calcium, magnesium and ammonium.
- Chelates micronutrients: they bind iron, zinc and other micronutrients, which can keep them available, especially on alkaline soils.
- Improves soil structure and water holding, particularly in sandy and low-organic-matter soils.
- Stimulates root growth in some trials.
Responses tend to be largest on poor, sandy or low-organic-matter soils and smallest on fertile soils rich in organic matter. Be wary of any product that promises fixed yield increases.
Product forms
| Form | Typical use |
|---|---|
| Potassium humate flakes or powder | Dissolved for fertigation, foliar sprays or liquid blends |
| Granular humic | Spread alone or blended with granular fertilizers |
| Liquid humic and fulvic | Ready to use in irrigation and sprays |
| Humic-coated fertilizers | Urea, NPK or other granules coated with humic material |
Why the test method matters
This is the most important point for buyers. The same product can show very different humic acid percentages depending on how it was tested. Older methods often overstate the content, while the standardised method published as ISO 19822 gives lower, more comparable figures. When you compare offers, ask:
- Which test method was used for humic and fulvic acid content?
- Is the figure on a dry-matter or as-is basis?
- What are the potassium, moisture and insoluble residue levels?
- What is the raw material?
Two products both labelled “70% humic acid” may not be comparable unless they were tested the same way.
What to check before you buy
- Humic and fulvic acid content, with the test method.
- Solubility and insoluble residue for fertigation.
- Potassium content and pH.
- Heavy metals: limits apply in many markets, so ask for the analysis.
- Registration and organic approval in your country.
- Packaging, quantity and delivery terms.
Our guide to requesting a bulk commodity quotation explains how to set out an enquiry.
Sourcing through Agromer
Agromer has traded agricultural commodities internationally since 1985 from Saint-Avertin, France. Our organic fertilizer range includes manure pellets, liquid biofertilizers, blood and bone fertilizer and lithothamnium. Humic products are not a standard line, but you can send an enquiry with your specification and we will tell you plainly whether we can help.
Frequently asked questions
What is humic acid fertilizer used for?
To improve soil’s ability to hold nutrients and water, to keep micronutrients available and to support root growth. It is used alongside fertilizers, not instead of them.
What is the difference between humic and fulvic acid?
Humic acid molecules are larger and dissolve only in alkaline conditions. Fulvic acid molecules are smaller and dissolve at any pH.
Where does humic acid come from?
Most commercial humic acid comes from leonardite, an oxidised form of lignite. Lignite, peat and compost are also used.
Is humic acid organic?
It comes from natural organic matter, and many humic products are approved for organic farming. Approval depends on the product and your certifier.
Why do humic acid percentages vary so much between suppliers?
Because different test methods give very different results. Always ask which method was used, and compare products tested the same way.
Can humic acid replace fertilizer?
No. It supplies little nitrogen, phosphate or potash. It helps the soil and the crop make better use of the nutrients you apply.