Carbon sequestration, micro-organisms behaviour and soil structure in soil amended with anaerobic digested matter

Mr Robin Béghin-Tanneau1, Dr Frédéric Guérin2, Dr Maritxu Guiresse3, Dr Didier Kleiber1, Dr Javier-David Scheiner1,2

1Unité de Recherche Pathologie et Génétique Végétales (PPGV), Université de Toulouse, INP- PURPAN, Toulouse, France, 2Geosciences Environnement Toulouse UMR 5563 & UR 234 IRD, Université Paul-Sabatier, Toulouse, France, 3EcoLab, Université de Toulouse, CNRS, INPT, UPS, Toulouse, France

Anaerobic digestion of organic matter by micro-organisms results in the production of biogas, a renewable fuel, and in residues broadly called digestates. Digestates are a complex mixture of water and organic and inorganic substances including nutrients. So far, anaerobic digestion is well identified as an attractive renewable energy pathway but the use of digestates as an amendment is still under evaluation. In this study, we compared soil structure amended with undigested or digested organic matter and investigated its relationships to the composition of these amendments, soil carbon sequestration and the behaviour of microorganisms. The experiment was carried out in the laboratory with sieved soil samples. Soil structure was evaluated by measuring aggregate stability under various wetting conditions and energies which assessed soil’s susceptibility to crusting and erosion. The composition of organic matter was assessed through its granulometry, specific surface area, fiber fractionation and Rock-Eval Pyrolysis. Soil carbon sequestration was calculated from measurements of soil CO2 productions. The 13C tracer technique, using natural abundance differences between C3 and C4 plants, has been used to separate native soil organic matter derived CO2 productions (from C3 plants) and amendments derived CO2 productions (from C4 plants) to explain C sequestration by measuring amendments stability and induced changes in native soil organic matter mineralization after amendment addition. Micro-organisms behaviour was assessed through changes in viable soil microbial communities after amendment incorporation. Fingerprints of the microbial communities within soil profile was determined via phospholipid fatty-acid (PLFA) analysis which elucidates their phenotypic structure. Experiments are incomplete at the moment. Preliminary results showed statistical differences of soil C sequestration and aggregates stability after undigested and digested EOM addition in soil. Firsts PLFA analysis showed differences after undigested and digested EOM addition in soil. The link between these elements remains to be determined at the end of the experiment.


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