## 4 Discussion  
The Effects of Different Treatments on the Characteristics of Straw Decomposition and the Content of Humic-like Substance Components  
The decomposition rate of straw undergoes a rapid change from 0 to 90 days, followed by a more gradual change from 90 to 150 days. This pattern demonstrates fast decomposition in the early stages and slower decomposition in the later stages, aligning with previous research findings [22]. The decline in carbon content in straw correlates with the decrease in mass loss rate during decomposition. Initially, microorganisms consume soluble sugars, organic carbon, and other easily decomposable components in straw, causing a rapid drop in carbon content. Additionally, higher summer temperatures promote microbial growth, influencing straw decomposition rates. As the more resistant components like lignin break down only after the easily degradable ones are consumed, the availability of carbon sources for microorganisms diminishes, leading to a gradual slowdown in straw decomposition [34]. As the decomposition time increased, the straw decomposed gradually, with noticeable differences observed among various treatments. By the end of the 150-day experiment, the mass loss rate followed the order T2 \(>\) T3 \(>\) T4 \(>\) T1. Previous studies have indicated that different fertilization treatments enhance straw decomposition primarily by boosting the abundance of microorganisms. The introduction of livestock and poultry manure contributes to the diversity of microorganisms, stimulates the secretion of biological enzymes by these microorganisms, and consequently accelerates the decomposition of straw [35; 36]. Additionally, the incorporation of livestock and poultry manure supplies ample energy and nutrients to microorganisms, influencing the quality loss rate of straw. This study found that the decomposition effect of straw mixed with livestock and poultry manure was highest, with chicken manure showing better treatment results compared to cow manure due to its higher nutrient content. Additionally, some organic matter in cow manure is challenging for microorganisms to decompose and utilize, impacting the overall decomposition process of straw. The trend in carbon release rate from straw closely mirrored the mass loss of straw. Carbon released during straw decomposition either contributes to soil organic matter synthesis or is decomposed into CO2 and released into the atmosphere by soil organisms [37]. The rate of carbon release during the decomposition process of straw returning to the field varies significantly across different studies. This variation may be attributed to factors such as the intrinsic properties of the straw, the method of returning it to the field, the length of the straw, the characteristics of the mulching soil, and the prevailing climatic conditions [38]. Corn straw is rich in lignin, which serves as a fundamental element in the formation of humus [39]. Through the degradation of lignin, various compounds like phenolic and aliphatic compounds contribute to the creation of humus-like substances [40]. Some scholars have proposed the lignin theory to elucidate the decomposition of corn stalks and the creation of humic substances. According to this theory, lignin serves as the fundamental structural component for the generation of humic acids. Initially, humic-like acids (HAs) are produced, followed by the transformation into fulvic acids (FAs) through additional oxidation [41]. The humus is primarily composed of humic acid-like substances (HLAs), fulvic acid-like substances (FLAs), and relatively large humin-like substances (HMLs), which are quantified by their organic carbon content. The water-soluble substance (WSS) content of corn stalks is high, with WSS being a key component in the microbial degradation of organic matter [42]. This study found that the content of water-stable aggregates (WSSs) in residual straw was significantly higher compared to other treatments.