Humic Substances like humic acid are being promoted as important organic material that should be added to gardens to improve soil health. All gardeners have heard of humus, that friable, black gold that we all wish we had. Since you can’t buy humus, companies have started to provide the next best thing – humic substances.
You might think that humus and humic substances are the same thing, but they are not. We need to treat these two as separate products and evaluate each on its own merits.
In this post I will do a deep dive underground to better understand humic substances, humic acid and humates.
What is Humus?
I have described humus in detail in another post called What is Humus? For the purpose of this discussion humus can be thought of as the end product of decomposing organic matter. As organic matter decomposes the chemical structure gets smaller and smaller until most of the nutrients have been extracted and carbon is left.
It is the organic component of the black crumbly earth that you find in undisturbed forests.
The current scientific thinking is that humus does not really exist, and I have discussed this in detail in Humus Does Not Exist – Says New Study. The main reason for this is that chemists can only see it and study it once it’s extracted from soil using highly alkaline solutions.
For the purposes of this discussion I’ll use the traditional definition for humus; recently decomposed organic matter.
What Are Humic Substances
Humic substances are a group of compounds that can be extracted from soil, peat and coal. Humic substances can be further subdivided into three fractions, humic acids, fulvic acids, and humin, depending on the extraction procedure. Unlike other chemicals we are used to dealing with, these are very complex molecular systems that can’t be well defined.
The other important point is that the molecular structure in soil is much different than the molecular structure in the extracted material and we have no idea how one relates to the other. If this sounds complicated – it is. Put simply, we have no idea what structural form humus or humic acid take in soil. Therefore we are unable to say that any commercial product is the same as humus.
We don’t even know if humic acid exists in soil – it probably doesn’t.
Humates are also promoted a lot. Humate is the solid form of humic acid, so both have basically the same chemical properties. However, at least one company sells humate which is nothing more than crushed coal.
Commercially the focus has been on humic acid.
The Benefits of Humic Substances
There is no doubt that humus and humic substances in soil play a very important role. These are just some of the benefits they provide.
- Enhance the growth of soil microbes
- Help retain water and chelate nutrients
- Improve compaction and porosity
- Mitigate stress from pollutants and salts
- Improve plant growth
For these reason companies are starting to promote the idea of using commercial humic substances as organic fertilizers for building soil health.
The important question that needs to be asked is, do these commercial products provide the same benefits as the natural substances in soil?
Source of Commercial Humic Acid
Extracting humic acid from soil is too costly for commercial purposes. A much cheaper source are various types of coal, namely, lignite and leonardite. How does coal relate to the soft crumbly humus we know in soil? Humus is recently decomposed organic matter. Coal is also decomposed organic matter, but it is a much older form and its been compressed underground for millions of years.
How does the chemical structure of humus and coal compare? Therein lies the problem. Chemists can’t characterize the chemical structure of humus. They can only extract it and this process destroys its natural structure. Humic acid can be extracted from both coal and soil, but the resulting products are different. In fact, the end product depends very much on how it is extracted.
Many sources make it sound as if commercial humic acid is a natural, organic, material for your garden. It might be accepted as organic by certification organizations, but there is nothing natural about it. Companies can’t even confirm that the chemical structure looks anything like the material in soil.
I don’t understand how it can be considered organic? It is created through a chemical process not unlike those used to make many synthetic chemicals.
Benefits of Humus vs Commercial Humic Acid
Here is the marketing logic that is used to promote these products. Humus in soil provides many benefits as discussed above. Commercial extracts from coal produce humic acid. Therefore commercial products also provide the same benefits as humus.
Clearly this is flawed logic. Science has shown that humus in soil is beneficial, but science has not shown that the commercial product is beneficial, and since the two are chemically different, we can’t make an assumption just because a similar name is used for both.
The other problem is that there are many sources of coal and different extraction procedures are used to produce products, and the end results are not characterized enough to allow a consumer to compare one product to another, or even one batch to another. The industry currently relies entirely of consumer trust and the assumption that anything called humic acid is good for the garden.
That does not mean commercial humic acid does not work, but it does mean that it is impossible for a consumer to know if any product works.
Do Commercial Humic Acid Products Work?
A recent review published in 2018 said, “There is currently not enough research to explain possible mechanisms and accurately predict when (commercial) humic materials might prove beneficial”.
A meta analysis looking at many studies found inconsistent results. Some studies showed an increase in growth of 15-25%, but half the studies showed no increase in growth. When the source was compost, they performed better than when sourced from coal. High rates of application were generally required, but such rates were not cost effective for farmers.
Another review had this to say, “Humic products have been used in cropland agriculture for several decades, but lack of widespread credibility has restricted their use to small proportions of farmers.” It goes on to discuss the limitations which include a lack of positive field studies.
In 2002, a search for studies supporting the use of humic acid on turf, found only one study which reported that “of the 14 non-nutritional growth enhancers studied, including several humic acid and humate products, none affected bentgrass root length or root numbers. ”
Iowa State University looked at root growth for soybean and corn in laboratory trials and found mixed results. “These effects seem to depend on the concentration and source of the substance and on the plant species. ” Humic acid increased potato yields and quality, but only three of the brands tested had an effect. The researchers “caution potato growers who want to apply humic acid as a soil amendment to work with reputable companies that provide a consistent material and can supply unbiased data showing that their product works under local conditions.”
Dr. Daniel Fernandez, an expert on hydroponics had this to say, ” The literature (for hydroponics) is also quite consistent in that the largest effects are often seen on root growth rather than on shoot growth or mass.”
There seems to be very limited research showing commercial products work. Results are inconsistent and depend very much on the product used. This should be no surprise because there is no standardization of products.
Humic Acid Adds Carbon to Soil
Another claimed benefit of these products is that they add stable carbon to soil, increasing the organic matter in soil. And adding carbon to soil is good for the environment because this is sequestered carbon.
If we mine coal, convert it to humic acid and them add it to soil, we are best only moving sequestered carbon around. The amount of sequestered carbon is not increased. But we also have to think about the carbon that is turned into CO2 during the processing stage and shipping the material. Rather than being good for the environment, using these products actually adds CO2 to the air.
How much carbon is added to soil? A typical application adds about 15 lbs/acre. Compare that to the residue of a typical corn crop of 4,000 lb/acre. The amount is insignificant.
Humic Acid Options
Commercial humic acid is available in two basic forms; liquid and solid.
I discussed the liquid products when I discussed the use of lawn thatch reducers and liquid soil aeration. The claimed active ingredient of many of these products is humic acid and these products don’t work.
Liquid humic acid is not going to be very effective since the amount of humic acid applied is far to small to improve soil.
Solid humic acid makes a bit more sense since you are applying a larger amount of the product, per given area, provided that you apply enough. The solid material is also less expensive.
Does Humic Acid Work?
Maybe – but nobody knows.
The few studies that have been done are not encouraging and the manufacturers of these products are not commissioning studies to verify that their product works.
The commercial products don’t resemble natural humus or humic acid found in soil. Any benefits that are ascribed to natural humus can’t honestly be applied to commercial products. That leaves the industry with a problem – a product that has not been shown to work.
Unfortunately consumers are easily confused. They know humus is good for the garden, and readily accept that a product called humic acid, even if it is chemically manufactured from coal, also works.
As far as home gardens go, there is no science to support its use.
If you want to add organic matter to soil, use traditional material, like manure and compost. We know they work.