For those of you still recovering from the trauma of chemistry class back in school, please bear with the next few paragraphs. The topic of this article is humic acids, a complex subject even for a Ph.D. (which your author is not), so a little scientific background is required. We'll keep it short and basic before moving on to look at some of the practical benefits touted by manufacturers offering these materials.
The first order of business is to identify what humic substances are. As defined by the Humic Products Trade Association (http://www.humictrade.org), "Humic substances are the natural, dark-colored humified remains of decayed biomatter, ubiquitous in the environment as major components of natural organic matter in soils, water and sediments, with the highest concentrations found in lake sediments, peat and geological deposits of low-rank brown coals, bituminous coals and shales."
Humic products are most commonly but not exclusively derived from Leonardite, a lignite coal that is close enough to the surface that it has oxidized and can be mined. These materials look pretty crude, but they are chemically complex.
"The molecular structure of humic substances is unknown because they are devoid of a regularly recurring, extended skeletal entity," according to the HPTA. "They are a unique class of environmental biochemicals because their essence resides in the combination of their extreme molecular heterogeneity, complexity and pronounced chemical reactivity."
Humic substances are comprised mainly of humic acids (soluble in water only at higher pH levels) and fulvic acids (soluble at any pH level), as well as humin, which is not soluble in water. Humic acid tends to be darker than fulvic acid, but there are other key differences, as well.
"Fulvic acids are the smallest molecular form of humic acid molecules," explains Brian Galbraith, president of Humate International, which offers humate and other related soil products. "Over time, the fulvic acid molecules grow, or polymerize, and basically become larger and larger by attaching one to another and these larger forms of the molecules are called humic acids."
Galbraith says the progression takes a very long time and what begins as small molecules of dead plant material gets larger and forms fulvic acid and then humic acid, "until you get coal, which is just straight carbon chains with no [chemical] activity."
While both have the word "acid" in their name, Galbraith stresses that this is because of their molecular structure rather than their acidity.
"They are not acids in the sense of a sulfuric acid, or anything like that," he says. Their molecular structure makes them quite reactive, so in the soil they react with a variety of difference substances such as minerals and metals, he adds.
While humic acids generally share certain characteristics like this, there are many differences between various types and forms. "Humic acids can vary from site to site fairly significantly in their concentrations of humic and fulvic acids," says Joel Simmons, president of EarthWorks, which has been working with the substances for 25 years and includes humic acid as a component in every one of its products. "There are many different sources of raw materials and methods used to extract humic acids so there can be great variation in them. There's just such a wide spectrum of humic acids."
If all of this sounds confusing to you, you're not alone. "Humic acid is very interesting, because many people, including some manufacturers, don't know exactly what it is or how best to use it," Simmons says. "There are so many people jumping on the humic acid bandwagon thinking that it's some sort of silver bullet."
He dismisses some manufacturers' claims that their products contain only humic acid and no fulvic acid (or vice versa). "Most of those kinds of claims aren't even possible; they're outrageous," Simmons says.
That's not to say the benefits are not proven: "There is breadth of information - there's tons of real information," on humic acid, Simmons says.
"Humic acid is one of those areas where there are a lot of claims, but how many of them are founded in science is a whole different ball game," agrees Christopher S. Gray Sr., product marketing manager with LebanonTurf. In a quest to be able to put out verifiable information, he says LebanonTurf assigned a staff researcher to do nothing but investigate the role of humic acids in turfgrass.
"Many of the claims out there have been extrapolated from agriculture research, and people say, 'Well, if it does this for rice or beans, it must be able to do it for turf.' Well, that's not necessarily the case," Gray explains. "We need studies dedicated to turf that address each individual claim about humic acids, so people can have confidence in what they can do and what they can't do. I think that will make humic acid much more acceptable in our field. ... I think it's an area that's really going to grow in the next 10 years."
Don Sutton, North America agriculture sales manager with AMCOL, says that wild claims in the past have hurt the reputation of humic acid, and that education is needed.
"I would say there's a lot of skepticism in the market, in part because of past claims that humic acid is going to cure all problems," he observes. "We don't see it that way; we think humic acid can be a helpful part of a program."
Sutton feels greater scientific study of humic acid will help provide users with greater confidence in the benefits these substances can provide.
"We have invested heavily in research, not just to show improved crops or stronger turf," Sutton says. "We're investing to determine what's happening on the cellular level inside the plants to determine what's going on that's causing these responses. Right now a lot of people will agree that humic acid works, but right now nobody has really been able to answer how it works."
What it does do
"It's a carbon-rich soil amendment that can positively affect the soil chemistry as well as the soil microbial activity," explains John Pope, territory manager with The Andersons, boiling humic acid down to its essence. "One of the biggest things it does is help plants use applied nutrients more efficiently, particularly phosphorus and nitrogen. It also can increase the water-holding capacity and water retention in the soil, which in turn increases retention of the soluble chemical fertilizer in the soil."
So, basically, humic acid keeps moisture and nutrients in the rootzone longer, and helps the plant make better use of them.
"Our humate, because of the very high CEC [cation exchange capacity], will grab ahold of metal ions like iron, manganese, copper and so on," Galbraith says. "So one benefit is it will hold those micronutrients in the rootzone and make them more available to the plant."
Applying humate then can be an alternative for lawn pros trying to lower the soil pH on clients' properties in order to give plants access to such micronutrients tied up because of high pH levels.
Humates can also help to aggregate the soil structure, Galbraith says. "You get a more open soil, which helps to get oxygen down in the soil," he explains. "Microorganisms and earthworms and other things in the soil need to have oxygen."
Adds Gray: "Some of the things we found that humic acid can do - with real science behind it - is that it serves as a soil microbial stimulator and an organic chelator." When you have a sand high content, there are certain things missing in that growing medium that humic acid helps to provide and fix.
"For example, high sand situations naturally have a very low cation exchange capacity. Humic acid can substantially increase that," says Gray.
Dan Lee with Biofeed Solutions says that improved cation exchange capacity is one of the most obvious benefits of humic acids. "What that results in is a high availability of the soil-bound nutrients," he explains. "It's been well documented that humic acids aid in nutrient absorption in plants, especially when applied as a foliar to the leaf."
Biofeed Solutions' products differ from some others on the market because they contain no mined Leonardite or humate products, Lee says.
Sutton says: "What we've seen is just overall improvement in how plants deal with environmental stress, whether it's drought or heat or a combination of both. We've also seen development of larger root systems - basically building a bigger, stronger plant."
How humics are used
In addition to improving CEC and nutrient availability, humic acids can also help turf combat stress, but are not a quick fix.
"When stressful conditions start to arise, what you find out is that grass treated with humic acid will outperform untreated turf," Gray says. "Once the stress is already induced, you can't just spray on the humic acid after that. It's like the flu shot, you can't get the flu shot after you've gotten the flu."
Pope says that humic acids and other biostimulants need to be used as part of a regular program prior to stress in order to get the most benefit.
"That's how I see it working best," seconds Sutton. An ongoing program including humic acid will also help other products applied throughout the season to work better, he says, because the turf will be healthier. "And the humic acid molecule has a lot of receptor sites that nutrients such as nitrogen, phosphorus and potassium can attach to, so it's likely helping the applied fertilizer be retained in the soil and utilized by the plant much better," Sutton adds.
Simmons says that humic acids function best as "synergistic agents" rather than being applied on their own. EarthWorks' products that are heavier on humic acid are used mainly as soil conditioners; other products include less humic acid but use it to activate other biological and chemical reactions in the soil.
"When you add multiple forms of carbon, you really have some biological food sources," Simmons explains, noting the company uses items such as sugars, fish, kelp meal, fermentation products and compost for this purpose.
Humic acids can be solid (the most direct form) or liquid (after being made soluble through a reaction with an alkaline material). Humate International, for example, offers its products in solid, liquid and soluble powder forms.
Lee says that Biofeed Solution's humic acid products, such as Soil-Plus, can be tank mixed in sprayers with other fertilizers as well as turf protection products.
"By and large, they are safe to mix with anything," he states, reporting that some users have been able to cut their herbicide and insecticide rates by adding the company's product, because the humic acid chelates the minerals in the water in the tank, preventing them from inhibiting the effectiveness of the pesticides.
The Andersons offers Humic DG, which is produced using the company's dispersal granule technology.
"We've micronized the humate and then put it together back in a spreadable, dispersable pellet that can go through standard equipment," Pope explains, noting that this makes humic acid much easier to handle and apply. The raw mined product, on the other hand, is usually dusty and often doesn't go through spreaders very well, he adds. The process used by The Andersons also involves drying the humate, allowing it to be offered in blends with other fertilizers so it can be applied as part of a regular fertilizer program rather than as a separate application, Pope notes.
LebanonTurf is set to introduce two new products this year that incorporate humic acid, including a granular product blended with fertilizer to simplify the application process for superintendents. The company currently uses humic acid in some of its organic and synthetic products. "It makes our fertilizer a better value for the superintendent, because when you have an increased CEC the nutrients are more available to the plant," Gray says.
AMCOL is now offering a straight humic acid product with a very low pH that superintendents can blend themselves.
"It's tank mix-compatible with just about any fertilizer or plant protectants that they might be using," Sutton explains. Because of its benefits and versatility, he thinks there will be a growth in humic acid use in coming years.
Patrick White is a freelance writer based in Middlesex, Vt. and is a frequent contributor to Turf magazine. Contact him at firstname.lastname@example.org.