Fractionation and characterization of humic substance fractions with different molecular weights, Obtained from animal wastes

The humic substances contained in an animal organic waste were extracted and the total extract separated into three humic fractions with different molecular weights (low, F1 10(3); medium, F2 with molecular weights ranging from 10(3) to 10(4); and high, F3 10(4)). The C content was highest in F2, the same fraction also showing the lowest N content. The molecular weight of the humic fractions influenced the electrical conductivity, the highest molecular weight resulting in the lowest degree of electrical conductivity. Membrane-controlled ultrafiltration (the method used to separate the various fractions from the whole extract) was also suitable for purifying such enzymes as phosphatase and beta-glucosidase: the total activity obtained from the three fractions was considerably greater than that determined in the whole extract. Pyrolysis-gas chromatography (PyGC) applied to the whole extract and humic fractions showed that in the F3 fraction (highest molecular weight) benzene was the major fragment while furfural was the major fragment of F1 (lowest molecular weight). For this reason, the humification index benzene/toluene indicates that the fraction with the highest molecular weight was the most humified while the furfural/pyrrole ratio indicates that the fraction with the lowest molecular weight was the most degradable. The whole extract and the fraction F1 had a negative effect on seed germination when the concentration was equivalent to 100 mg kg(-1) of C, while the germination index was higher than that of the control when only 10 mg kg(-1) were sued. F2 fraction had a positive effect on germination regardless of the concentration used. When 10 mg kg(-1) of C of the humic substances studied were added to the nutrient solution for growth experiments with maize plants, F3 led to increases in root weight and F2 led to increases in shoot weight. An inhibitor effect was observed for fraction F1