Effects of soil compost load on water-extractable organic matter content and its UV- and fluorescence-based compositional characteristics

Abstract

The application of compost increases soil organic matter (SOM) content; however, there is a lack of information on the short- and long-term effects of compost application on the dynamics of labile SOM pools in compost-amended soils in semiarid region. The goal of this study is to distinguish between parameters that can be used for investigating the accumulative effects of compost application and parameters that are sensitive for short-term changes but diminish with time. To address this goal, we focused on (1) the effects of compost application rates on short-term dynamics of soil contents of microbial biomass carbon (MBC), cold water-extractable organic carbon (WEOC), and hot water-extractable organic carbon (HWEOC), respectively, and (2) composition of WEOC and HWEOC characterized using (i) absorbance at 254 nm (Abs₂₅₄) representing the presence of aromatic components and (ii) fluorescence spectroscopy of excitation–emission matrices coupled with parallel factor analysis. Soil samples were taken from a long-term field experiment in semiarid region, which investigated the effects of the annual load of a cattle manure-based compost (at rates of 0, 20, 40, or 60 m³ ha⁻¹ year⁻¹) on soil properties and crop performance. C concentrations in soil water extracts were found to be sensitive indicators of compost-load effect on soil organic carbon content. Compost dose had a strong short-term (2 weeks) impact on MBC, but no long-term (over months and years) effect was observed. Of the variables examined in the short term, the MBC, WEOC, and Abs₂₅₄ values of the extracts were found to be the most responsive to compost load. The proportion of the fluorescent constituents out of the WEOC and HWEOC decreased with compost dose. UV- and fluorescence-spectroscopy were found to be useful means to characterize the influence of compost load on the composition of water-extractable organic matter and hot water-extractable organic matter in semiarid region.