Active chemical fractions with high fungistatic activity of humic‐like substances obtained via different extraction solvents

BACKGROUND: Humic‐like substances (HULIS) for use in controlling soil‐borne diseases have been a research focus, but obtaining HULIS with high fungistatic activity via different extraction solvents has been challenging. In this work, three solvents were selected to extract HULIS from weathered coal. Inhibition rates against phytopathogens were used to evaluate the fungistatic activities of HULIS. Element contents (C, N, S, and O) and carbon‐13‐cross polarization magic‐angle spinning nuclear magnetic resonance (¹³C‐CP‐MAS NMR) spectra were used to evaluate the chemical composition. The relationships between the chemical compositions and fungistatic activities were assessed by redundancy analysis (RDA) and partial least squares regression (PLSR). RESULTS: The results showed that HULIS extracted with different solvents varied in the element contents, organic carbon structures and fungistatic activities. HULIS extracted with potassium hydroxide–ethanol had the highest content of C, the lowest contents of N and O, and the highest fungistatic activities (up to 71.86%). Consistent results through RDA and PLSR shows that C and S had positive effects on the fungistatic activity, while N and O had negative effects. Aliphatic C in HULIS had positive effects on the fungistatic activity, while the aromatic fraction and anomeric C had negative effects. CONCLUSION: In summary, different solvents extracted different fractions from weather coal. Mixed solvents with organic and inorganic solvents were more beneficial for extracting active fractions with higher fungistatic activity of HULIS from weather coal. The results of this work provide a good theoretical basis for the application of HULIS extracted from weathered coal. © 2019 Society of Chemical Industry