Influence on the growth of four different plant species and inhibition of pathogenic fungi by humic acids from soil and lignite in relation to their chemical structure

Humic acids (HA) represent the major fraction of humic substances, which are supramolecular mixtures formed through humification of organic matter in soils, sediments, and natural waters. Rich in carboxylic and phenolic groups, HA influence soil fertility, nutrient availability, plant growth, and stress tolerance. Their biostimulant effects depend on origin, chemical structure, and concentration, and, although still poorly understood, their fungistatic activity against phytopathogenic fungi is i