Humic acid has long been a familiar term in agriculture, often mentioned as a beneficial component of soil health and plant nutrition. It appears on the labels of soil amendments and as standalone products, promising to enhance nutrient uptake and improve soil structure. But recent scientific insights suggest that humic acid, at least as we've traditionally understood it, might not exist in the way we thought. The very methods used to measure it may have been creating it all along, raising intriguing questions about what humic substances really are—and how they truly work in the soil.
The Humic Acid Paradox: Creating What We Measure
Humic substances, the complex mixture of organic compounds found in soil, compost, and peat, have been studied for over a century. Traditionally, they were divided into three categories—humic acids, fulvic acids, and humins—based on their solubility. Scientists believed that humic acid played a distinct role in improving soil structure and nutrient cycling.
However, recent advances in analytical techniques, such as nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry, have upended this view. These methods reveal that humic substances are not composed of discrete, well-defined molecules but are instead a chaotic assortment of organic compounds. Even more unsettling is the realization that "humic acid," as an isolated substance, might not naturally occur in soils at all.
The kicker? What we’ve been calling humic acid is largely an artifact of the laboratory extraction process. The classic method used to isolate humic acid involves treating soil or compost with a strong alkaline solution, which breaks down organic matter in a way that doesn’t reflect what’s happening in natural soils. This extraction creates a mixture of compounds that we’ve conveniently labeled "humic acid," but these compounds don’t exist in this form outside the lab. In other words, by measuring humic acid, we’ve actually been creating it.
This revelation challenges decades of assumptions. The substance that has been extracted and quantified in labs is, in fact, a product of the chemical process used to define it. What we thought was a natural and crucial component of soil health may be, in large part, a byproduct of our methods.
What Does This Mean for Agriculture?
Does this mean that humic acid is just a myth, and that everything sold under its name is based on faulty science? Not quite. While humic acid as a distinct compound might not exist naturally in soils, humic substances as a whole are still vital to soil ecosystems. Even though we’ve been wrong about the chemistry, the biological impact is real.
The organic compounds that make up humic substances—whether or not we can call them "humic acid"—clearly benefit soil and plant health. Numerous studies show that well-composted organic matter rich in these substances improves soil structure, water retention, and nutrient availability. Plant growth is often enhanced, and crops become more resilient in the face of environmental stress. It’s not about one molecule, but rather a complex, ever-changing collection of organic compounds working together.
The issue is more about our understanding and language than the benefits. The same compost that we thought was rich in humic acid still contains an array of organic molecules that work wonders for soil and plants. The laboratory-defined "humic acid" may be a fabrication of our testing methods, but the value of these humic substances remains.
Humic Substances: Still Key to Soil Health
While our scientific understanding of humic acid has evolved, and the substance itself may not exist in its previously imagined form, humic substances are still critical for soil health. Humic substances have been shown to clearly improve plant growth, nutrient uptake, and soil structure.
The humic acid content of organic fertilizers and composts remains an important measure of quality with higher humic acid contents indicating greater compost maturity and quality. High quality organic fertilizers such as composted Black Soldier Fly frass are particularly high in humic substances. Diptia, our flagship organic fertilizers has an average of 5.4% ‘humic acid’ and a remarkable 9% fulvic acid. In a paper published just last month Cai and co-authors found that in a composting system Black Soldier fly larvae “increases the proportion of fulvic-like acid by 45.53–48.77 % and humic-like acid by 12.29–14.27 %.”
Notice these authors using the term ‘humic-like acids.’ Science does not always get it right the first time but in biology in particular simple stories often hide wonderful complexity. Ultimately, we know that composting and using quality soil amendments that foster the natural breakdown of organic material will continue to provide the benefits we’ve long attributed to humic acid—whether or not we ever find it in its pure form.
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