EFFECTS OF HUMIC SUBSTANCES ON PLANT GROWTH
Beneficial effects of humic substances (HS) on plants at various physiological growth stages have been reported in the literature. However, most of the research had focused on seeds and seedlings. HS enhanced imbibition and germination of seeds of wheat, maize and barley. Increase in respiration and enzyme activity was observed. A number of investigators reported enhanced root initiation and growth. HS application to the nutrient solutions resulted in beneficial effects on tomato, pepper, wheat, maize, millet, bean and geranium. The optimum level of HS is controversial but usually ranges from 50 to 500 mgL-1. Effects similar to those of IBA on rooting of mung beans were observed in water extracts of composts. Foliar or nutrient solution application of HS also enhanced shoot growth. Enhanced growth of young tomato, bigonia and sugar beet leaves resulted from foliar spray of HS. Nutrient uptake, height of shoots and the number of flowers of cucumber plants increased as a result of the presence of fulvic acid at concentrations of up to 300 mgL-1 in the nutrient solution. Metal-organo complexes of Fe, Zn an Mn with peat, lignite or manure significantly increased micronutrient uptake and yields of several field crops. A significant number of investigations that focus on plant-hormone like effects of HS were discussed, as well as the various possible mechanisms that give rise to the effects described.
Chen, Y. and Solovitch, T. (1988). EFFECTS OF HUMIC SUBSTANCES ON PLANT GROWTH. Acta Hortic. 221, 412-412