Humates: snake oil or valuable resource?

While humates are promoted as an almost magic potion by some, sub-standard products have battered their reputation. Glenneis Erasmus talked to several agriculturists to find out what they are, how to use them and how to ensure product quality.

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Among the rising number of “environmentally friendly” soil improvers on the market, humic and fulvic acid are shrouded in mystery and debate. Reading the literature, one can find a reference to their failure for every reference to their success.
To debunk the myths, Gerda Burger from SA Biofarm starts by differentiating between humin, humic acid and fulvic acid.

“All of these are humates, which are the end-product of decomposition,” she explains. “Fulvic acid is soluble in water under all pH conditions, and is light yellow to brown-yellow. Humic acid is dark brown or grey-black, and soluble in water with a high pH. Humin is a very dark black and isn’t water-soluble at any pH.”

Effects and uses: fulvic acid
Fulvic acid’s small molecules carry minerals from plant surfaces into plant tissues via the roots, stems and leaves. Dr Robert Pettit, Associate Professor Emeritus at Texas A&M University, says it’s a key ingredient in high quality foliar fertilisers. Gerda adds that immobile minerals in plants – such as iron, calcium and magnesium – bind to it to be carried to where they’re needed. Plants react to fulvic acid as they react to auxins, the growth hormones that promote cell division and elongation. The acid also stimulates oxygen uptake, making plants more heat and drought resistant.

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Humic acid and humin
Humic acid has a larger, more complex molecular structure than fulvic acid and plants don’t absorb it as easily. Gerda says its main benefit is its effect on the soil. “It helps improve the soil structure and, by binding with clay particles to form stable organic complexes, increases the soil’s cation exchange capacity. Humic acid can hold up to 16 times more minerals than clay, making them more readily available to plants.”

By penetrating between clay particles, humic acid can release potassium for use by plants. It also complexes with elements such as phosphorous, zinc and calcium so that they interact less with other elements and the soil. It even complexes with nitrogen, making it less volatile and less prone to leaching. Humic acids also help to clean soil of toxins, pesticides and heavy metals, and stimulates microorganisms.

Humin has the highest molecular weight and therefore plant growth responds to it much more slowly. Among the products giving humates a bad reputation, some contain humin rather than humic acids.  “Although humin isn’t soluble, it can be ground into very fine particles to be put in a suspension,” explains a source from a renowned chemical company, who doesn’t want to be named. “Farmers can’t tell the difference just by looking.”

Quality problems
Humates’ bad reputation may be due to a lack of legislative control. “There are loopholes because humic and fulvic acids are seen as soil conditioners, not as fertilisers,” explains the source. “As a result, fly-by-night companies sold inferior humate products, with a humic acid content under 3%, for the same price as respectable companies’ products containing over 10% humic acid.”

Particularly problematic, explains John Riggs, CEO of Cape Aquatic Humates, are imported products, usually from the East, where dilution, gravity and other criteria are measured inaccurately or not at all. He advises farmers to send them to an independent, certified laboratory to check quality. Dr Louis de Lange of MBB Engineering counters that different laboratories use different extraction methods and might get different results. Farmers need a standard to measure products against.

Riggs doesn’t see legislation as a solution. “If developed countries such as the US, Europe and Japan can’t regulate the quality of organic acids, how can South Africa manage to do so? There’s no classification or legislation, or even political will regarding certification standards for organic agriculture, biological farming, biodynamic farming and everything in between.”

‘How’ is as important as ‘what’
But farmers must use the product correctly. Gerda stresses. “We cut fertiliser use by 30% on the farm where I worked, but humic and fulvic acids should be seen as another tool to improve efficiency. Use them as part of an integrated production management system, not a stand-alone intervention.” The products’ effectiveness will also depend on soil conditions, application methods and the specific product used.

“Organic acids might help loosen fixed nutrients and make them more available to plants,” says Gerda, “but farmers should still analyse soil and plants to ensure there are enough nutrients for optimal production, and that the plants can absorb them. Whether you use these products or not, your first priority should always be to restore the nutrient balance of your soil.”

Because of the huge differences in opinion over which products to use, Cornelius Oosthuysen from SA Biofarm advises farmers to first test products on small plots and keep a control area to measure whether they’re working. “Farmers are flooded with new information and products all the time – always test products before using them on a large scale to determine whether the claims are true and whether the products are suitable  for your production conditions,” he says.

De Lange and Riggs agree. “Proper trials help farmers calculate the costs:benefit ratio,” says Riggs. “You need to know what’s going on in your soil – if you’re not measuring the effect of your inputs, you’re not managing your soil and are a ‘hobbyist’ rather than a businessperson.” For more information visit

Going back to the source

The effectiveness of the organic acid product will also depend on its source material, how it was extracted, and how it’s used. In the article Humic & Fulvic Acids: the Black Gold of Agriculture, which appeared in New Ag International (see, Dr Geoff Perry, general manager of Omnia Specialities Australia, claims products extracted from low-grade coal sources like leonardite are far better than those extracted from organic matter such as compost, manure or plant waste.

Dr Perry says organic-based products might show benefits fast, but the effect is much lower and fades quickly, sometimes within a few weeks (see Box: Humic and fulvic acid contents of various materials). Theo Geldenhuys from Bio-Farm Solutions promotes using humate products that meet the International Soil Association Standards. “The leonardite-based humic products have a complex molecular structure which makes them almost five times stronger than other humic matter. A kilogram has the same humic and fulvic acid content as 30t manure or fish emulsion, and a higher carbon content.”

John Riggs, CEO of Cape Aquatic Humates, disagrees. “These companies are trying to sell their product. I believe humic substances from plant material and water are just as effective. It’s almost like compost tea, which quite often works very well when combined properly with good cultivation practices – whether totally organic or biological farming methods.”  He doesn’t want to divulge the extraction and production methods Cape Aquatic Humates uses, but emphasises they’re much more natural than extraction from leonardite. Manure only contains 5% to 15% humic and fulvic acids.

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