Soil organic matter characterisation using alkali and water extraction, and its relation to soil properties

• Published in: Geoderma Regional 2022-03, Vol.28, p.e00469, Article e00469
• Main Authors: Jakab, Gergely, Vancsik, Anna, Filep, Tibor, Madarász, Balázs, Zacháry, Dóra, Ringer, Marianna, Ujházy, Noémi, Szalai, Zoltán
• Format: Article
• Language: English
• Subjects: Conservation tillage; Excitation emission matrix; Fulvic acid fraction; Luvisols; Soil microbiome; Water-extractable organic matter
• ISSN: 2352-0094; 2352-0094
• DOI: 10.1016/j.geodrs.2021.e00469

The optical and fluorescence properties of dissolved organic matter are widely used to estimate the soil organic matter composition. To do so, various absorbance and fluorescence properties of soil extracts are investigated using various indicators such as the alkali-extracted fulvic acid (FA) fraction and the water-extractable organic matter (WEOM) content. Nevertheless, it is not yet clear whether different indicators from various matrixes are directly comparable. The present study compares the fluorescence and optical properties of the same soil under various tillage systems for fourteen years using the isolated FA and WEOM fractions. The soil is a haplic Luvisol under ploughing (PT) and conservation tillage (CT) in subhumid conditions. The extractions were characterised using UV–vis spectroscopy and the excitation emission matrix. Microbiome-related soil properties were also investigated. The microbial biomass carbon and cellulose decomposition did not register differences between the two tillage systems. The WEOM carbon content was related to the organic matter content of the soil (R2 = 0.87), whereas that of the FA was not. The WEOM indicated more humified composition under CT. In contrast, the FA did not show differences in humification between the two tillage systems, but revealed higher aromaticity under CT. Although the measured absorbance and fluorescence values were standardised by the extracted carbon content or the index calculations, the results differed significantly between the FA and WEOM fractions. Compared to the FA, in the present case, the WEOM is a better indicator of organic matter composition changes due to land use shift, providing an economical and fast method for routine soil organic matter characterisation •Conservation tillage increases the total and both water and alkali soluble organic carbon contents.•Water-extracted organic matter reflects the changes better than the alkali extraction.•Both extract characteristics are independent of the microbiome and the physico-chemical soil properties.