The effect of humic and fulvic acids on the growth and efficiency of nitrogen fixation ofAzotobacter chroococcum

Humic acid in the form of sodium humate and fulvic acid markedly increased the growth and efficiency of nitrogen fixation ofAzotobacter chroococcum. Fulvic acid proved more effective than the sodium humate. The effectiveness of these substances was more pronounced in increasing the number of cells than affecting the nitrogen fixation. The increases in growth and nitrogen fixation were in direct proportion to the quantities of sodium humate and fulvic acid applied up to 500 and 700 ppm respectively. Thereafter the growth was restricted, although it was not inhibited even at 1,400 ppm.