## 4 Discussion
### Effects of Different Treatments on Soil Organic Carbon Components
This difference may be attributed to the fact that more components were converted into humin and humic acid during the straw decomposition process, while fewer components were transformed into fulvic acid. Additionally, soil microorganisms play a role in continuously decomposing and utilizing amino acids and other nitrogen-containing compounds present in fulvic acid components with simple molecular structures and high activity, leading to a continuous transformation into humic acid and ultimately resulting in a relatively higher humic acid content. [PERSON] and [PERSON]'s research demonstrated that soil humus components increased as straw decomposed, resulting in the renewal of soil humus [44]. The percentage content of HA (PQ) in alkali-soluble humus is an important indicator to measure the degree of humification of humus [61]. This study demonstrated that adding manure to straw treatment significantly increased the PQ value of soil humus compared to other methods. The application of manure improved soil microbial activity and enhanced the mineralization decomposition of corn stalks, leading to increased soil humus formation. The complexity of soil humus structure is determined by the \(\Delta\)logK value, with higher values indicating simpler structures [62]. Some studies have shown that returning organic materials like straw to the field can activate and rejuvenate humus [63]. This study demonstrated that the \(\Delta\)logK values of soil humic acid and fulvic acid were notably enhanced with the addition of animal manure. This suggests that the structure of soil humic acid and fulvic acid could be simplified and revitalized through the use of animal manure. This phenomenon may be attributed to the return of livestock manure to the field, which effectively stimulated the decomposition and conversion of corn straw by microorganisms, leading to the formation of new soil humus with a relatively simpler structure. During the process of straw decomposition, the conversion of straw carbon in soil plays a direct role in influencing the content of soil organic carbon pools. Soil dissolved organic carbon (DOC) is considered the most dynamic form of organic carbon in soil, possessing the ability to dissolve, adsorb, and transfer readily. This organic carbon source serves as a direct nutrient for microorganisms [64]. In this study, the soil DOC content significantly increased with the addition of straw mixed with livestock and poultry manure compared to T1 treatment. This is attributed to the release and dissolution of water-soluble organic matter into the soil during the straw decomposition process. Additionally, the presence of livestock and poultry manure creates a low C/N environment, which is conductive for microorganism survival and promotes the decomposition of straw, leading to the release of dissolved substances [65]. Soil ROC, the active component of soil that is prone to oxidation and decomposition, was found to have significantly increased soil ROC content with the addition of livestock and poultry manure treatment compared to T1 treatment. The introduction of foreign organic matter, organic matter, and straw into the soil leads to decomposition by microorganisms, resulting in decomposition products with relatively low oxidation stability, making them a key source of easily oxidized organic carbon. MBC, the organic carbon present in living microorganisms within the soil, represents the most dynamic and active organic carbon in soil ROC [66]. The application of animal manure served as a carbon source for the soil, stimulating microbial activity and aiding in straw decomposition. This decomposition, in turn, supplied nutrients for soil microorganisms, enhancing their abundance and activity. Consequently, the MBC content in the soil increased [67]. The continuous input of carbon and nitrogen in livestock manure and straw stimulates the growth and proliferation of microorganisms. The increase in microbial abundance enhances their ability to decompose organic matter, creating a virtuous cycle [68; 69].