Comparison of chemical and biological methods to measure humic acid content in Pennisetum sp.

The humic and fulvic acids in Pennisetum sp. were compared with chemical and biological methods. Cellulose, hemicellulose, and lignin were degraded to produce humic acid and fulvic acid with nitric acid, hydrochloric acid, acetic acid, oxalic acid, and ammonia. The humic acid content was the highest when using 10.0% ammonia, followed by 37.5% nitric acid and 37.5% hydrochloric acid, while oxalic acid and acetic acid were the lowest. Bacillus subtilis, Mucor, Rhizopus, and Penicillium played a positive role in the formation of humic and fulvic acids. The degradation degree of lignin was the highest when using Rhizopus. The total humic acid contents were 1.45 and 1.29 times that of 10.0% ammonia under Rhizopus and Mucor fermentation, respectively, while the total humic acid contents were less than 10.0% ammonia under both B. subtilis and Penicillium fermentation. The content of fulvic acid using 37.5% nitric acid was 1.79 times that of Mucor fermentation, and the content of fulvic acid using 22.5% hydrochloric acid was 1.98 times that of Mucor fermentation.