LAUSR

Abstract This study was conducted to assess the humification degree in fulvic acids (FA) from different composts, and to reveal their roles after soil amending based on their excitation-emission matrices (EEM) of the fluorescence spectra and projection pursuit regression (PPR) analysis. Two peaks were detected in EEM spectra of FA from all composts, and three components were identified by the parallel factor analysis (PARAFAC) model. The assessment of the humification degree of FA using the ratios between the values of the percent fluorescence response in the visible and ultraviolet regions (PI,n/PII,n) generally agreed with that using the distributions of FA components (C1, C2 and C3). The PPR considering the parameters (PI,n/PII,n, C1, C2 and C3) further ranked the composts with similar of FA, and the FA humification degree decreased in the order: GW, TSW, LW and SW > CM, MSW, and PM > MC and KW. The results showed that the compositions of FA were similar to each other in composts from different materials, but there were distinct differences in the humification degree of FA owing to the different distributions of each component in composts. Therefore, based on the redistribution of components, a method for regulating the humification degree of FA during composting was presented. Furthermore, the suitable soil application of composts with different humification degrees was also demonstrated.