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Humic Acid

Humic acid is a humified organic fraction commercially extracted from leonardite, an oxidised soft brown coal intermediate between peat and lignite. It is the major component of soil organic matter in mature humus and is sold as a soil conditioner and biostimulant in powder, flake, granular and liquid forms. The most common formulation in Indian agriculture is potassium humate.

Composition

  • Primary source: leonardite (oxidised soft brown coal); alkaline digestion with potassium hydroxide produces potassium humate.
  • Typical commercial spec: 50-70% humic acid plus 8-12% K2O on a dry basis.
  • International minimum spec: 15% total humic extract, of which 7% humic acid (IHSS/EU benchmark).
  • Appearance: black, free-flowing powder or dark amber liquid.

Indian formulations are notified under the FCO biostimulant rules as soil conditioners.

Mode of action

Humic acid acts through several distinct mechanisms in soil. The high density of carboxyl and phenolic-hydroxyl groups raises cation-exchange capacity, reducing leaching of K, Ca, Mg and micronutrients. Bound metal cations are released slowly to the soil solution and to roots. Humic substances also stimulate root cell elongation and proliferation, enhance membrane permeability and improve soil aggregate stability. Unlike Fulvic Acid, humic acid precipitates at acid pH, so soil application is more effective than foliar use.

Target use and dose

  • Soil/drip application: 0.5-2 kg per acre, applied through drip irrigation or as basal incorporation.
  • Mixed with FYM or compost: improves nutrient retention.
  • Seed treatment: dilute solutions to coat seed before sowing.

Used across paddy (Humic Acid Paddy), cotton, sugarcane, banana, vegetables and orchards. Effects are largest on degraded soils with low organic matter and may be marginal on already-fertile soils.

Safety and regulatory status

FCO-notified as a plant biostimulant/soil conditioner. Non-toxic at field rates. Storage in dry conditions preserves product quality.

See also: Fulvic Acid, Humic Acid Paddy, Humic Fulvic Acid Input, Leonardite Soil Conditioner, Seaweed Extract, Vermicompost.

References

  1. Humic Acids and Humic Substance and Leonardite. humicacid.org technical reference.
  2. Humic Acids Crops Technical Report. USDA Agricultural Marketing Service.