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The following is an in-depth analysis involving an organic raw material with a curious name, leonardite. It owes its name to the American geologist Arthur Gray Leonard, the first director of the North Dakota Geological Survey, who significantly contributed with his research to the characterization of this material and its possible uses in agriculture. You can view through this link volume XVII (1963) of the “Proceedings of the North Dakota Academy of Science”, which contains a publication entitled “Humic Acids from Leonardite: a Soil Conditioner and Organic Fertilizer”, signed by the researchers Youngs and Frost, the source of the table below.

Leonardite as a source of humic substances

Leonardite originates from fossils and constitutes the most superficial layer of lignite deposits, a fossil carbon used mainly as fuel. Compared to lignite, leonardite is characterized by greater oxidation. On the other hand, from a compositional point of view, it stands out for its significant content of humic and fulvic acids, amounting to 30-80%, which make it a matrix suitable for the formulation of soil conditioners and organic fertilizers.

Its properties lie mainly in the stimulating effect on the microbial activity of the soil, in the ability to chelate nutrients, iron in particular, and in the stimulation of root growth. Furthermore, when used as fertilizer, it provides significant amounts of slow-release nitrogen.

The black gold of agriculture

Humic and fulvic acids interact with metal ions, oxides, hydroxides, mineral and organic compounds, including any pollutants, to form complexes soluble and insoluble in water, which favour the dissolution, mobilization and transport of metals and organic substances in soil and water, or – on the contrary – cause their accumulation in certain soil horizons. This latter ability may help reduce the toxicity of heavy metals. Humic substances also have positive effects on plant physiology, improving the structure and fertility of the soil and influencing the absorption of nutrients and the proliferation of roots, as well promoting the softness and porosity of the soil. The presence of auxins in humic substances is known, while the possible “auxin-like” action of these substances has not yet been sufficiently proven.

By virtue of all these very important properties and their dark colour, humic substances are also referred to as the “black gold of agriculture.”

There’s more than just humic and fulvic acids in leonardite

The table below (from Youngs and Frost, 1963) shows a comparison of the compositions of lignite and leonardite (values expressed as a percentage). As specified by the authors, the ash content of leonardite may vary widely from deposit to deposit, but it’s usually between 15 and 30% of dry matter.

Componente Leonardite Lignite
Ashes* 18,7 10,0
Hydrogen** 4,0 5,1
Carbon 65,2 72,8
Nitrogen 1,3 1,2
Oxygen 26,6 19,9
Sulphur 2,9 1,0

*of dry matter

**of dry matter, net of ashes

In reality, the analysis of Leonardites from different sources reveals the presence of numerous nutritional elements in addition to those shown in the table, including Potassium, Magnesium, Zinc, Iron, Manganese and Calcium, in varying quantities. An important characteristic of this organic matrix is its generally , which must be taken into account when evaluating t, which must be taken into account when evaluating its eligibility for soil distribution.

Leonardite can also be used in leaf distribution products with a biostimulant action.

Leonardite, as-is or in the form of biochar obtained by treating it at high temperatures, shows high effectiveness in immobilizing certain herbicides, such as atrazine.

Wefert recommendations

Black Humic, leonardite obtained exclusively as a by-product of mining activities, is a liquid soil conditioner containing a good supply of humic acids and fulvic acids, with an acidic pH (5.4) and allowed for use in organic farming. It produced many activities in the soil and secondly on plants. The humic and fulvic acids of Black Humic influence the development and growth of plants by acting as chelating agents for metal ions (Iron in particular), thus allowing an increase in photosynthesis. Administered at the roots, it acts on the ground, improving its cation exchange capacity, structure, permeability and softness. It also promotes the protection and absorption of nutrients, reduces salinityneutralizes the pH of alkaline soils and increases vegetative activity and resistance to abiotic stresses. Its ability to enhance the activity of growth factors makes it advisable to use it on the seeds and root system of seedlings before transplanting.