What is the difference between humic acid and fulvic acid in soil health?

Humic acid and fulvic acid are naturally occurring organic compounds found in soil. Humic acid is larger and less soluble, making it most effective at improving soil structure and long-term carbon storage. Fulvic acid is smaller, highly soluble, and moves rapidly into plant roots, driving immediate nutrient uptake. Together, they form the most biologically active fraction of soil organic matter.

How do humic acid and fulvic acid form in soil?

Both acids form through humification, where soil microorganisms break down plant residues and organic material over long periods. Fulvic acid represents an earlier stage of this transformation: lighter, more oxidised, and more soluble. Humic acid has undergone more extensive condensation, producing a denser, darker compound that binds tightly to soil particles.

Peat bogs are among the most concentrated natural sources of both acids. Waterlogged, low-oxygen conditions slow decomposition and allow humic substances to accumulate over millennia, making Nordic peat an exceptionally rich and consistent source for agricultural use.

What are the main structural differences?

Humic acid has a high molecular weight and is soluble only in alkaline conditions. Fulvic acid has a much lower molecular weight, more oxygen-containing functional groups, and remains soluble across the full pH range. Fulvic acid carries a higher density of carboxyl and hydroxyl groups, giving it a strong ability to chelate mineral nutrients such as iron, zinc, and manganese. Because it is small enough to pass through plant cell membranes, it can carry those nutrients directly into root cells.

Humic acid’s larger structure means it does not enter plant tissue. Instead, it aggregates soil particles into stable structures, holds water in pore spaces, and provides a long-term reservoir of carbon and nutrients.

How does each acid affect soil structure and water retention?

Humic acid is the more powerful of the two for improving soil structure. Its large molecules bridge mineral particles together, forming stable aggregates that improve aeration, reduce compaction, and increase the soil’s ability to hold water. Research published by the EU Joint Research Centre found that over 60% of EU soils are affected by at least one major degradation process, including organic carbon loss and compaction. Rebuilding humic acid levels is one of the most effective ways to reverse this trend.

Fulvic acid supports soil structure by stimulating microbial growth and improving the solubility of locked-up mineral nutrients, resulting in a more biologically active soil that retains both moisture and fertility more effectively over time.

Which is more effective for plant nutrient uptake?

Fulvic acid is more effective for direct plant nutrient uptake. Its small molecular size allows it to penetrate root cell membranes and carry chelated micronutrients with it. This is particularly valuable for micronutrients such as iron, which readily precipitates out of solution in neutral to alkaline soils. Fulvic acid binds these elements into stable, soluble complexes that roots can absorb directly.

Humic acid contributes through a different mechanism. By improving the cation exchange capacity (CEC) of soil, it increases the number of sites available to hold nutrient ions such as calcium, magnesium, and potassium. It also stimulates root elongation, expanding the volume of soil a plant can explore for nutrients.

Can humic acid and fulvic acid be used together?

Yes, they are highly complementary and work best when combined. Fulvic acid acts as the fast-acting component, rapidly improving nutrient solubility and stimulating root development. Humic acid builds the structural and biological foundation that makes those improvements sustainable season after season. Together, they also support soil carbon sequestration — humic acid as a stable, long-lived carbon form, and fulvic acid feeding the microbial community that drives formation of new humic compounds.

Products such as NeoTerra™ soil conditioners deliver both humic and fulvic fractions from 100% RPP-certified Nordic peat, free from heavy metals, weed seeds, and pathogens, making them suitable for both conventional and organic farming systems.

What sources are richest in humic and fulvic acids?

The richest natural sources are peat, leonardite, lignite, and vermicompost. Nordic peat is particularly valued because cold climate, high rainfall, and oxygen-limited decomposition preserve an exceptional density of intact humic compounds. Leonardite delivers very high humic acid concentrations but typically lower fulvic acid fractions than peat. Vermicompost and matured composts also contain meaningful levels, though concentrations vary by feedstock and processing.

Research conducted through the Neova Agro R&D programme at the University of Jyväskylä has confirmed high auxin, cytokinin, and gibberellic acid activity in Nordic peat extracts, underscoring why the source of humic substances is as important as their concentration. Responsible extraction under certifications such as RPP ensures sourcing from already-degraded sites rather than intact, high-conservation-value peatlands.