Humic acid is the dark, alkali-soluble fraction of humus, the stable organic matter that forms as plant and animal residues decompose. It is one of the main reasons rich soils are dark, crumbly and good at holding water and nutrients.
Where humic acid comes from
When organic matter breaks down, microbes turn most of it into CO2. A small part is rebuilt into large, complex molecules that resist further decay. These humic substances can last in soil for decades to centuries. The same process, over geological time, makes peat, lignite and leonardite rich in humic substances, which is why these materials are the main commercial source.
Humic acid, fulvic acid and humin
Humic substances are classed by how they dissolve, not by a single chemical formula:
| Fraction | Soluble in alkali | Soluble in acid | Typical use |
|---|---|---|---|
| Fulvic acid | Yes | Yes | Foliar sprays, fertigation, liquid blends |
| Humic acid | Yes | No (precipitates below about pH 2) | Soil conditioning, granular and soluble fertilizers |
| Humin | No | No | Remains in soil; not extracted commercially |
Commercial products follow the same logic. Insoluble humic acid is used in soil and in granules. Reacting it with potassium or sodium hydroxide gives soluble potassium humate and sodium humate. Fulvic acid is the fraction that stays in solution after acidification.
What humic acid does in soil
- Holds nutrients. Its many carboxyl and phenolic groups give it a high cation exchange capacity, so it holds potassium, calcium, magnesium and ammonium where roots can reach them.
- Keeps micronutrients available. It forms complexes with iron, zinc and manganese that are less likely to lock up in alkaline soil.
- Builds structure. It binds mineral particles into crumbs, which improves aeration, drainage and water holding.
- Buffers pH and salts. It moderates sudden changes in soil pH and salt concentration.
- Feeds soil life. It is a slow, stable carbon source for the microbial community.
How growers use it
Humic acid is applied as granules or powder before planting, blended into NPK and organic fertilizer granules, or used as soluble humates through drip and flood irrigation. Our carbon fertilizers combine humic acid with a modest NPK base for growers who want to rebuild soil organic carbon. For the wider picture, see soil organic carbon.
How to choose a humic product
| You want to… | Choose |
|---|---|
| Improve soil before planting | Humic acid granules or a carbon base fertilizer |
| Add humic carbon through irrigation | Potassium humate or a humic water-soluble fertilizer |
| Spray on leaves | Fulvic acid or potassium fulvate |
| Make your own granules or liquids | Humic acid or potassium humate raw material, with TDS and COA |
FAQ
Is humic acid the same as humus?
No. Humus is all the stable, decomposed organic matter in soil. Humic acid is one fraction of it: the part that dissolves in alkali and precipitates when the solution is acidified.
What is the difference between humic acid and fulvic acid?
Fulvic acid is the smaller, more oxidised fraction that stays soluble at any pH. Humic acid is larger and precipitates below about pH 2. Fulvic acid suits foliar sprays; humic acid works mainly in the soil.
Is humic acid a fertilizer?
Not on its own. It supplies stable carbon and improves how soil holds and releases nutrients, but contains little N, P or K. It is used alongside, or blended into, fertilizers.
Where does commercial humic acid come from?
Mostly from leonardite and lignite, oxidised low-rank coals that are rich in humic substances. It is extracted with alkali to make soluble humates such as potassium and sodium humate.