Abstract
The effects of humic substances (HS) and their basic components, such as humic acid (HA) and fulvic acid (FA), were evaluated for their ability to control Fusarium oxysporum f. sp. cucumerinum, as well as to improve vegetative growth of cucumber plants under pathogen pressure, in greenhouse conditions. Three concentrations ranging from 50, 100 and 150 ppm for each HS, HA and FA were tested for their efficacy in reducing pathogen growth. In vitro, FA extracted from green compost of plant residues and biogas manure significantly reduced (P = 0.05) pathogen growth at a concentration of 150 ppm compared to the control. FA extracted from plant residues at concentrations of 150 ppm reduced disease severity significantly (84.7%) in relation to other treatments. A significant increase in dehydrogenase enzyme activities and total number of microorganisms in soil were obtained by HA extracted from biogas manure with respect to other treatments. All applications significantly improved growth parameters of cucumber plants in the presence of natural inoculum, with the effects of HA treatments being more pronounced.