Speaker
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The application of organic waste products (OWP) and the sowing of winter cover crops are agronomic levers to improve soil health. Anaerobic digestion of OWP is now a common practice and, as biogas is considered a renewable energy source, its development is encouraged by the European Union. Biogas digestate, a by-product of this process, is increasingly produced and recycled on agricultural land.
Studies on the transfer of dissolved organic carbon (DOC) in the soil after digestate application are scarce, despite the potential interest in carbon sequestration through the transfer of DOC to the subsoil and stabilization on the mineral phase (Rumpel and Kögel-Knabner, 2011) or the risk of co-transport of contaminants to groundwater, which poses a threat to the health of aquatic ecosystems (Dunnivant et al., 1992). In a previous lysimeter study conducted over 9 years (Didelot at al., submitted 2024), the effect of digestate application was compared to its original pig slurry in association with different winter crops (wheat, mustard, multispecies) on DOC concentrations and fluxes. Higher topsoil DOC concentrations were observed each year for the digestate modality, possibly related to crop root development. Crops can provide organic matter through the decomposition of residues (roots, leaves, stems) and root exudates (Kalbitz et al., 2000). Root exudates are low molecular weight compounds (Nguyen, 2009) and can contribute to the DOC pool. In annual plants, 30-60% of the carbon fixed by photosynthesis is translocated to the roots and up to 70% of this carbon can be released to the soil (Neumann and Römheld, 2000). Scaglia et al. (2015) highlighted an auxin-like effect in pig slurry digestate, which could potentially lead to biostimulation of root growth. Thus, the additional DOC measured after digestate application could be due to an increased production of root exudates through a potential auxin-like effect of digestate.
A 13C-labelling experiment was set up in soil columns mixed with digestate, pig slurry and a mineral treatment, and containing mustard plants. The plants were grown under greenhouse conditions and twice a week, for 3 h, they were placed in airtight chambers into which 13C-CO2 was injected. After a total duration of 2.5 months of multipulse labelling, drainage was induced. Samples of drained water, soil, shoot (leaves, flowers, stems) and roots were dried or freeze-dried and then finely ground before isotopic analysis of the 13C content using cavity ring-down spectroscopy. The amount of rhizodeposition will be calculated using a model for 13C in the soil solution. The aim of this experiment is to accurately assess the contribution of rhizodeposition from the plant to the DOC pool in the soil-plant-digestate system.
References:
Didelot, A.F., Jardé, E., Morvan, T., Lemoine C., Gaillard, F., Hamelin, G., Jaffrezic, A. Disentangling the effects of applying pig slurry or its digestate to winter wheat or a catch crop on dissolved C fluxes. (Submitted to Agriculture, Ecosystems & Environment in January 2024)
Dunnivant, F.M., Jardine, P.M., Taylor, D.L., McCarthy, J.F., 1992. Cotransport of cadmium and hexachlorobiphenyl by dissolved organic carbon through columns containing aquifer material. Environ. Sci. Technol. 26, 360–368. https://doi.org/10.1021/es00026a018
Kalbitz, K., Solinger, S., Park, J.-H., Michalzik, B., Matzner, E., 2000. CONTROLS ON THE DYNAMICS OF DISSOLVED ORGANIC MATTER IN SOILS: A REVIEW. Soil Science 165, 277.
Neumann, G., Römheld, V., 2000. The release of root exudates as affected by the plant’s physiological status. The Rhizosphere: Biochemistry and organic substances at the soil-plant interface 41–93.
Nguyen, C., 2009. Rhizodeposition of Organic C by Plant: Mechanisms and Controls, in: Lichtfouse, E., Navarrete, M., Debaeke, P., Véronique, S., Alberola, C. (Eds.), Sustainable Agriculture. Springer Netherlands, Dordrecht, pp. 97–123. https://doi.org/10.1007/978-90-481-2666-8_9
Rumpel, C., Kögel-Knabner, I., 2011. Deep soil organic matter—a key but poorly understood component of terrestrial C cycle. Plant Soil 338, 143–158. https://doi.org/10.1007/s11104-010-0391-5
Scaglia, B., Pognani, M., Adani, F., 2015. Evaluation of hormone-like activity of the dissolved organic matter fraction (DOM) of compost and digestate. Science of The Total Environment 514, 314–321. https://doi.org/10.1016/j.scitotenv.2015.02.009
| Keywords | Digestate; DOC; plant; contribution; 13C labelling |
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