Effect of swine biogas slurry application on soil dissolved organic matter (DOM) content and fluorescence characteristics

The application of biogas slurry as an organic fertilizer is a promising method for utilizing breeding manure wastewater. At present, the impact of biogas slurry on the properties of organic matter in soil is not clear. In this study, a pot experiment in which chemical fertilizers were replaced with biogas slurry from a swine farm was performed. The fluorescence spectra combined with parallel factor (PARAFAC) analysis and principal component analysis (PCA) were used to explore the influence of biogas slurry on the protein and humic substance contents in the dissolved organic matter (DOM) in soil. The results showed that there were two proteins (component 3 (C3) and component 4 (C4)) and two humic substances ( component 1 (C1) and component 2 (C2)) in the DOM of the experimental soil. The application of swine biogas slurry can significantly increase the content of DOM in soil, but the increase was weakened with extended time. Compared with the CKA, the biogas slurry significantly increased the C1, C2, C3 and C4 contents in the initial stage by 116.17%, 76.41%, 578.71% and 278.13%, respectively. Within 28 days of planting corn, proteins with simple molecular structure in the DOM in the soil began to be transformed into humic substances with high molecular weight and more complex molecular structures. On the 60th day, the contents of C1 and C2 in the DOM of the treated treatments soil increased by 13.72%-34.40% and 5.05%-17.78% respectively, and tyrosine content decreased by 90.11%-94.41%. This study provides a new perspective on the effects of biogas slurry application on soil properties and sustainable utilization of soil.