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Leonardite-based soil conditioners

Leonardite is a soft, highly oxidised brown coal that lies between peat and lignite in the coalification series. It is the principal commercial source of humic substances worldwide, and the raw material for the majority of humic and fulvic acid products sold as soil conditioners and biostimulants.

Composition

  • Origin: highly oxidised brown coal, dark brown to black, easily friable
  • Humic substance content: 40-85% combined humic and fulvic acids on dry weight
  • Mineral fraction: clay, silicate and trace minerals depending on deposit
  • Indian sources: most leonardite used in Indian product manufacturing is imported, with the United States (North Dakota), China and Eastern Europe as major sources

Direct-applied leonardite is rarely used as such; it is most often processed into derived products before sale.

Mode of action

Leonardite supplies humic substances that act through three concurrent mechanisms once incorporated into soil. The high carboxyl and phenolic-hydroxyl functional density raises cation-exchange capacity, retaining K, Ca, Mg and micronutrients against leaching. The humic and fulvic fractions chelate metal cations, keeping them plant-available across a range of pH. And the colloidal particles improve soil aggregate stability, infiltration and water retention.

Target use and forms

The commercial route is to alkaline-extract the leonardite with potassium hydroxide and yield three downstream products:

  • Potassium humate (powder, flake or liquid) for drip and broadcast application; see Humic Acid and Humic Fulvic Acid Input.
  • Fulvic acid concentrate for foliar and micronutrient-carrier use; see Fulvic Acid.
  • Granulated humic blends combined with NPK and micronutrient fertilisers.

Typical dose for the extracted products is 0.5-2 kg per acre per season, applied through drip or as basal incorporation, often distributed in two or three split applications.

Safety and regulatory status

Leonardite and its derived humic products are notified in India under the FCO biostimulant/soil-conditioner schedule. Non-toxic at field rates; the raw material is mined and processed in dry industrial settings.

See also: Humic Acid, Fulvic Acid, Humic Fulvic Acid Input, Humic Acid Paddy, Gypsum In Groundnut.

References

  1. Humic Acids and Fulvic Acids. Acidos Humicos technical reference.
  2. Humic Acids and Humic Substance and Leonardite. humicacid.org.