Different Responses of Soil Dissolved Organic Matter to Different Types of Compost

Abstract

This study explored the responses of soil dissolved organic matter (DOM) to the application of different types of compost using a soil sample without compost as a control. Ultraviolet and fluorescence spectrum technology and EEM-PARAFAC was used to analyze DOM structure and driving factors in soil added with different proportion of cow dung compost (SCC), food and kitchen waste compost (SFC), and sludge compost (SCC). Compared with the control group, contents of AN, NH4+-N, DOC, and SOM in soil added with compost were significantly increased, and contents of SOM and DOC increased with the increasing of compost amount. When added compost in the same proportion, contents of AN, NO3--N, and DOC in SCC and SFC were significantly higher than those in SSC, while contents of NH4+-N and SOM were higher in SSC. The results of spectral analysis showed that the structure of conjugated benzene ring, hydrophobic component, quinone group, and chromogenic component in DOM of soil added with compost were significantly increased, the transition of unsaturated organic molecule (π→π*) was more active, the molecular weight of DOM increased, and the degree of humification was enhanced. When the amount of compost added is 5%, the influence of food and kitchen waste compost on DOM structure was greatest among three types of compost. At 10% and 20%, sludge compost had the greatest impact on DOM structure. The results of EEM-PARAFAC analysis showed that the relative content of fulvic acid-like substances with low molecular in DOM of soil added with compost was increased, while the relative content of proteoid-like substances decreased. 2D-COS analysis showed that compost affected the change order of fluorescence components in DOM. SCC and SFC were as follows:proteoid-like > fulvic acid-like > humus-like; in SSC, it was fulvic acid-like > proteoid-like > humus-like. The enhance of humification and the decrease of relative content of protein-like substances in DOM were related to increased DOC and AN, the relative content of humus-like in low molecular weight was positively correlated with the content of NO3--N, and the relative content of macromolecule fulvic acid-like was increased due to the input of SOM from compost.