Benefits to Turfgrass from Humic Acid Applications
What is humic acid?
Humic acid products have been around for several decades in various forms. Since there is some confusion among turf professionals with respect to what benefits humic acids actually provide to turfgrass, some background information and a review of published literature can help clarify things.
Humic substances are the dark-colored substances that remain after the natural degradation of biomatter that are resistant to further degradation. Certain types of coal or substances that are similar to coal but younger are typically used to manufacture humic acid products. The concentration of humic acid in different humic substances varies considerably and manufacturers often claim that their source is better than another. My discussions with leading researchers on humic substances indicate that the humic acid you get from one source isn’t better than another as long the humic acid is extracted prior to formulation. In research settings, the most successful products are formulated from humic acid that has been extracted from the raw material. These are then formulated into both liquid and dry products. Some products are simply processed raw humic substances with no extraction taking place beforehand, which tend to be less effective.
How does humic help turf and soil?
There are many claims about what humic acid applications do for turf and soil. Examples include: increasing organic matter, increasing CEC, increased germination, increased micronutrient availability, etc. However, the most consistently observed effect from humic acid applications is a stimulatory effect, usually measured in root and shoot mass increases. A stimulated plant will have more demand for nutrients and therefore will interact with more nutrients, water, and biology in the soil. This leads to claims of better nutrient use efficiency and availability. Even though the mechanism that causes these effects isn’t fully understood, some leading theories propose that humic acids have a hormone-like effect in the plant, leading to some of the observed benefits. It should be noted that humic acid will not affect the organic matter or CEC values in the soil as the application rates used do not provide enough organic matter to alter those soil properties.
When does humic work best?
Typically, humic products work best in altered or difficult conditions although benefits can still be observed in normally productive soils. Sand-based greens and athletic fields are a prime target for humic product use. Several published studies have observed the stimulatory plant growth effect and subsequent benefits to the turf stand.