Biochar Regulates the Humification of Kitchen Waste and the Effects of the Humic Acid Structure of Products on Black Soil

Kitchen waste is a misplaced resource that is characterized by a high organic matter content, high water content, and a tendency to rot easily. Biochar is a black solid substance produced under high-temperature, anaerobic conditions using agricultural organic wastes as the raw material. It possesses a large specific surface area, a loose and porous structure, and functional groups, which confer high thermal stability and strong adsorption capabilities. However, little is known about how humic products made from biochar affect the composition and structure of soil humus. To solve the above problems, this study carried out a two-year outdoor field experiment by means of element analysis, infrared spectroscopy, and differential thermal analysis (0.4 kg/m2 (W4), 0.8 kg/m2 (W8), 1.2 kg/m2 (W12), 1.6 kg/m2 (W16), and 2.0 kg/m2 (W20)); CK was the blank control (no application). The samples were collected one year and two years after they returned to the field. The results showed that the application of organic materials facilitated the accumulation of soil organic carbon (SOC) and increased the total nitrogen (TN) content. The highest SOC content in the W20 treatment was 12.39 g/kg and 14.67 g/kg in one and two years, respectively. The maximum relative HA content in the W20 treatment was 22.99% one year after returning to the field. The PQ value (the ratio of HA/(fulvic acid (FA) + HA)) for the W20 treatment was 88.21%. The W20 treatment greatly increased the SOC and humus carbon contents. Compared with the CK treatment, all the organic materials applied for one year improved the structure of the humic acid to varying degrees, increased the degree of oxidation, reduced the degree of condensation and thermal stability of the HA in the soil, and gradually simplified the structure of the humic acid; among all the treatments, the W20 treatment had the greatest effect.