A Physicochemical and Biological Composite Environment for the Humification of Crop Straw in Compost

To examine the humification characteristics of crop residues, three types of crop residues—wheat, maize, and rice—were selected for experimentation. The latter two were subjected to steam explosion (SE) and nitrogen addition SE, respectively. Each of the three types of straw was inoculated in accordance with a specific microbial addition protocol. Furthermore, environmental controls, including the oxygen concentration and temperature type, were employed to enhance the variability of the samples. The results demonstrate statistically significant discrepancies in the concentrations of humic acid (HA) and fulvic acid (FA) between the three samples. Following a 96 h composting process, the highest concentrations of fulvic acid (FA) and humic acid (HA) in the samples were recorded at 10.4% and 15.8%, respectively. This result indicates the successful conversion of crop straw into a high-quality humic acid fertilizer product. Infrared spectroscopy data indicate that the breaking of carbon–carbon bonds and the ring opening, as well as the substitution of benzene rings, occurred during composting, and FA and HA substances were gradually formed. The results indicate that humus production is subject to raw materials, the pre-treatment of materials, the differentiation of strains, and methods of controlling environmental factors.