An adapted sequential chemical fractionation coupled with UV and fluorescence spectroscopy for calcareous soil organic matter study after compost amendment

authors

• Mouloubou Olsen Rainness
• Prudent Pascale
• Mounier Stéphane
• Boudenne Jean Luc
• Abaker Madi Guirema
• Théraulaz Frédéric

keywords

• Biowaste valorization
• Sequential extraction
• Soil organic carbon
• Spectroscopic analysis

document type

abstract

This paper aims to improve the understanding of organic amendments distribution on different fractions of soil organic matter (SOM) and the knowledge of processes controlling the temporal evolution of organic matter (OM) in the first layer of a calcareous soil of two adjacent plots, one control and one treated with 3kgm-2 of organic amendment. An appropriate fractionation procedure of SOM, consisting in sequential extractions by water, hydrochloric acid, sodium hydroxide and potassium pyrophosphate extractions, was applied. Dissolved organic carbon (DOC), UV and fluorescence spectroscopic properties of organic matter reveal quantitative and qualitative aspects. Spectral indexes such as SUVA254 (specific UV absorbance), E2/E3 and FI (fluorescence index) were used to examine annual changes of SOM in the different fractions.Extractions with pyrophosphate, and in a lesser amount with sodium hydroxide, represented the major part of DOC, for both control and treated soils. Yields of sequential extractions ranged from 16.1% to 16.4% of TOC for these two soils. Compost inputs resulted in evolution of quantitative and qualitative results, especially for water extractable organic matter (WEOM) and pyrophosphate extracts mainly during the first 3months of this field experiment. Study of annual changes of DOC, SUVA254 and E2/E3 index values in treated soil indicated a priming effect during the weeks after compost spreading, in relation with a revitalizing effect of microbial activity. Contributions of organo-mineral interactions and rainfall regulated WEOM amount throughout the year, and the activity of microbial communities in soil seemed to play a significant role on WEOM production. FI index values demonstrated microbial origin for WEOM, and for OM extracted either with acid or with sodium hydroxide. At the contrary, pyrophosphate extracts revealed that OM came essentially from terrestrial origin, which corresponds to the most complex and aromatic compounds. It was found that sodium hydroxide extracted less aromatic SOM, but higher molecular weight compounds. 3D fluorescence spectra revealed the presence of four main types of fluorophores according to the different extracts: humic, fulvic and marine-like compounds (A, C and M) common to all extracts, and lignin-like compounds (H) specific to pyrophosphate extracts only in treated soil at the beginning of the experiment due to initial compost effect. PCA on quantitative and qualitative data for WOEM fraction revealed essentially that meteorological aspects, with temperature and precipitation variations, were an important parameter over the year of experimentation, and that compost input impacted significantly WEOM amounts at the beginning of the experiment.

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