Effects of different conditioners on humus composition and humic acid structural characteristics in Black Soil under the combined application of pig manure and straw

Purpose: The objective of this work was to evaluate the variation in the amount and structure of humic acid (HA) after the application of different conditioners under the combined application of manure and straw. Methods This was measured by Fourier transform infrared (FTIR), fluorescence spectroscopies, and 13 C nuclear magnetic resonance ( 13 C CPMAS NMR). The experiment involved corn straw combined with pig manure (SZ), pig manure plus biochar (SCZ), pig manure plus boron slag (SBZ), pig manure plus biological agent (SJZ), and pig manure plus bio-organic fertilizer (SOZ), while corn straw only was used as control (SCK). Results The results demonstrated that pig manure combined with straw (PM-S) improved soil organic carbon (SOC), and the application of biochar and boron slag was the effect for improving the accumulation of SOC and humus C fractions. The elemental composition and 13 C CPMAS NMR results demonstrated that PM-S enhanced the ratio of H/C and the aliphatic C/aromatic C ratio of HA, reduced the O/C ratio, indicating enhanced aliphatic and conducive to simplifying HA molecular structure. Conclusion In conclusion, SCZ was more conducive to simplifying HA molecular structure and enhancing aliphatic and hydrophobic. However, the addition of biological agents and bio-organic fertilizer reduced the soil humification factor and is detrimental to soil organic carbon fixation.