Humic Acids: Hydrophilic or Hydrophobic?

Authored by John Pope

The past few weeks have been interesting, in that I’m hearing some of the same questions on my Spring travels that were being asked during my Winter trade show circuit.

There seems to be a great deal of chatter in the trade press and in trade advertising about humic acids causing water repellency in turf, especially in sand-based or constructed root zones.

In these ads, and in some discussions around “black layer,” the term “organic acids” is used very loosely. I have long felt that “organic acids” was a misunderstood term when related to bio-stimulants. We can have too much organic matter (thatch) but there cannot be too much humus in a soil. By definition, humic and fulvic acids are “organic acids.”

Most of the “organic acids” implicated in the coating of soil particles in trade advertising and press are created by pathogens in oxygen-poor (or hypoxic) soil environments. Hypoxic soils can lead to black layer, the organic acids becoming non-beneficial and hydrophobic (resistant to or avoiding wetting). Most of the “organic acids” illustrations of humic substances as hydrophobic molecules do not at all resemble actual humic or fulvic acid molecules from humates. Humates do not coat soil particles, but are actually held in soil solution.

The beneficial “organic acids” created by humic substances are extremely hydrophilic (or having a strong affinity for water). The polycyclic functional groups of humic acid molecules hold or “chelate” water. Humates actually hold many times their weight in moisture and they are not repellant, even when dry. This makes humic acids hydrophilic, not hydrophobic (resistant to or avoiding wetting).

For an example of humic substances remediating hydrophicity in soil, check out the article entitled “Remediation of Fire-Induced Hydrophobicity,” found here. This study details the after effects of a fire that burned through the San Bernadino National Forest in 2003. After wild fires, forest soils are strongly hydrophobic, in most cases making regeneration less than successful. This study details the remediation practices that were utilized to overcome post-fire hydrophicity.

Studies like this illustrate the fact that applications of a granular humic substance with a humate base have the ability to resolve hydrophobicity issues in short order.

Products like Humic DG, with its humate base, have the ability to support water movement through soil columns, and deal with water repellency by chelating soil moisture.

John Pope is a Territory Manager for The Andersons, Inc. Turf & Specialty Group, with a focus on high-tech, high-value solutions for the professional turf, horticulture and agriculture markets. John has been in the Plant Nutrient Industry for 33 years. He can be reached at: