Organic carbon, an indicator of soil and environmental health

On average, organic carbon represents about 55–60% of soil organic matter, which is why analytical determinations of organic carbon are empirically converted into organic matter content using the 1.724 factor, known as the Van Bemmelen factor. It is based on the assumption that soil organic matter contains approximately 58% organic carbon.

Organic carbon and soil organic matter are closely related but not interchangeable concepts: the former is an elemental measure, while the latter refers to a complex pool of substances that, in addition to carbon, may contain hydrogen, oxygen, nitrogen, phosphorus and sulfur.

Inorganic carbon primarily contributes to soil chemical properties, influencing pH (buffer effect) and serving as a slow-release source of calcium and magnesium, especially through dissolution processes.

Total soil carbon is the sum of its organic and inorganic fractions. Climate and weather strongly influence the balance between the two: high temperatures and drought, for example, promote organic matter mineralization and CO₂ release, increasing the inorganic fraction, while low temperatures and moisture slow microbial activity and favor the accumulation of organic carbon.

Soil organic matter:

• is an important reservoir of nutrients, especially nitrogen, phosphorus and sulfur, which are released through microbial mineralization;
• contributes to the formation and stabilization of macro- and micro-aggregates, improving soil structure, porosity, infiltration and water-holding capacity—especially in coarse-textured soils. This is due to polysaccharides and humic compounds acting as binding agents between sand, silt and clay particles. Such aggregation increases structural stability and reduces susceptibility to crusting and compaction;
• increases the cation exchange capacity, promoting the retention of nutrient cations (e.g., Ca²⁺, Mg²⁺, K⁺, NH₄⁺) and reducing leaching losses;
• stimulates microbial activity, enhancing plant availability of nutrients like Phosporous present in insoluble forms. Organic matter provides energy and carbon substrates for microorganisms, supporting high enzymatic activity and biodiversity within the soil microbiota. Its distribution within soil porosity promotes heterogeneous micro‑habitats capable of hosting different but complementary bacterial and fungal communities, limiting the dominance of pathogenic or parasitic species.

Agronomically, all this translates into higher yields, production stability and greater crop resilience to water, temperature and mechanical stress.
Environmentally, the accumulation of organic carbon in the soil is recognized as a climate mitigation factor, contributing to atmospheric CO₂ removal and the creation of long-term ecosystem services.

• a portion of carbon fixed by plants through photosynthesis is transferred to crop residues, roots and exudates which, after microbial decomposition, form more stable organic matter fractions;
• organic matter becomes incorporated into microaggregates, where limited oxygen and enzyme diffusion slows mineralization;
• adsorption onto clay minerals and other soil components produces organic matter with a slow turnover.

These processes reduce the share of organic carbon respired by microorganisms and the resulting CO₂ emissions, increasing carbon permanence in the soil. Sequestration capacity is controlled by climate, texture and mineralogy.

Organic carbon responds relatively quickly (years to decades) to these practices, whereas inorganic carbon is more influenced by climatic factors. Carbonation, the pedogenetic process leading to calcium carbonate precipitation, occurs in response to variations in temperature, pH, soil fauna activity and rainfall. Conversely, soil acidification can cause dissolution and CO₂ release.

From a climate mitigation standpoint, organic carbon is therefore the main target, as it is more directly manageable through agronomic practices, while the net sequestration potential of inorganic carbon remains uncertain.

In the medium to long term, managing soil organic carbon and organic matter represents a convergence point between productive needs, climate change adaptation, and emission mitigation strategies, within regenerative cropping systems capable of accumulating carbon, sustaining high yields and preserving soil functionality.

Its primary function is to restore the fertility of depleted soils by introducing microorganisms with specific activities such as nitrogen fixation, phosphorus solubilization, siderophore production and indole‑3‑acetic acid synthesis. Thanks to these microorganisms, the distributed organic matter and naturally provided humic acids, the soil improves its microbiota and increases microbial fertility, greatly benefiting crops.

Using Fertilsoil therefore results in an overall improvement of soil conditions and, consequently, of cultivated crops.