Humus (HS) is an important indicator of the nutrient quality of organic fertilisers. During the composting process, the addition of biochar and cotton straw wood vinegar liquid leads to changes in the internal environment of the heap, but the changes in the chemical properties of HS are not clear. The morphology of heavy metals (HMs) (e. g. Pb, Cr, Cd, Ni) was detected by flame atomic absorber, and Fourier transform infrared spectroscopy (FTIR) method and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) were used to characterise the complexes of HS and HMs from different angles. Meanwhile, mathematical statistics, correlation analysis and redundancy analysis (RDA) were; used to compare the decay indices (temperature, pH value), humification capacity (HS, fulvic acid (FA), huminic acid (HA), huminic acid and fulvic acid ratio (H/F)) and functional groups of the test groups. The results of the study showed that the wood vinegar liquid treatment could make the humification of the compost relatively high, and the peak located at 876 ~ 835 cm" was significantly enhanced, indicating the accumulation of aromatic structure, and the H/F finally reached more than 2. 3 in all cases. The HS content of the Tl biochar treatment was located between T4 and T3, and the H/F finally reached 3. 67. The passivation process of Cr by the Tl vs exchange state final passivation proportion to 2%. T4 treatment group in the Pb passivation process, the proportion of the final residue state was as high as 68%. Cd was more affected by T4, and eventually showed the transfer of 2%, 10% and 11% from the oxidation state to the exchange state, reduction state and residue state, respectively. However, the passivation of Ni by the addition of either biochar or wood vinegar liquid did not show any significant trend during the stacking process, and the proportions of exchange, reduced, oxidized and residual states were stable at 1 % ~ 2%, 5% ~ 7%, 26% ~ 35% and 56% ~ 68%, respectively, indicating that the effect of HS on Ni was relatively small in this experiment. FTIR further confirmed the role of HS as a core agronomic and carboxy late-rich basic properties of functional substances. The aromaticity of HS was gradually increased during the composting process, which enhanced the complexing ability with Pb, Cr and Cd ions. In addition, it was found that the wood vinegar liquid with a mass fraction of 1. 75% performed better overall in the composting process of the pig manure base. In summary, the following adsorption mechanisms existed for wood vinegar liquid and biochar; the special functional groups of wood vinegar liquid complexed with HMs ions; biochar relied mainly on adsorption with HMs; and the mechanism of Ni in composting may be more inclined to bind with nitrate ions. © 2023 Chinese Society of Agricultural Machinery. All rights reserved.
