Effects of returning corn straw incorporated with fungi, and fermented corn straw on soil humic acid structural characteristics

Aims During our previous laboratory incubation experiments, we found that the fungus ( Trichoderma reesei ( T . reesei )) has the best ability to transform corn straw into humic acid-like (HAL) substance. To further investigate whether the direct application of corn straw incorporated with T . reesei is as effective as the application of corn straw fermented with T . reesei in promoting the transformation and accumulation of stable soil organic matter components, a 720-day field experiment was established. Methods The field experiment involved four treatments applied to the soil at equal carbon mass: corn straw incorporated with T . reesei (CS-T), corn straw (CS), fermented corn straw treated by T . reesei (FCS-T), and blank control treatment (CK). The elemental analyzer, fluorescence and Fourier transform infrared spectroscopy, and thermogravimetric were used to comprehensively characterize the soil humic acid (HA) structure of the above treatments. Results The results showed that the CS-T treatment encouraged the decomposition of unstable components of soil HA at 30 days, and formed a relatively younger HA at 180 days. The FCS-T treatment directly formed soil HA with more aliphatic compounds between 30 and 360 days. After a long transformation and accumulation, the FCS-T treatment at 720 days increased the relative HA content to 29.3% and formed more aromatic and stable HA with the H/C ratio and fluorescence index of 1.257 and 0.618, respectively. Conclusions The application of FCS-T could be a more suitable practice than the direct application of corn straw to increase soil HA content and aromaticity, as well as to improve soil HA stability.