The impact of raw and composted food waste anaerobic digestates on soil organic carbon management: a pot study

Purpose Ever increasing food waste production has promoted anaerobic digestion and composting for its proper management, producing a relevant amount of recycled organic waste (OW) for possible agricultural uses. However, little is known regarding soil carbon management using this type of OW. Methods In this study, an anaerobic digestate from the wet digestion of food waste (WETD), and one from the dry-batch process (DRYD), along with their respective composts (WETC and DRYC), were utilized in a pot test over two growing cycles (84 + 84 days), with and without mineral nitrogen (N) fertilization, and were compared with a bio-waste compost (BWC) and a chemical reference (Chem). At the end of the two growth cycles (days 84 and 168), the ryegrass dry biomass (DW) and the N uptake were assessed. Results The pot soil was analyzed for soil organic carbon (SOC) and the potassium permanganate (KMnO4) oxidizable fraction (CL) as well as δ13C and Δ13C. At day 84, the SOC (g kg− 1) was the highest in DRYD and DRYC (8.53) > WETD and WETC (7.71) = BWC (7.86) > Chem (6.68), and performed similarly at day 168. At day 84, the carbon management index (CMI) was > 100% in all the organic treatments in comparison with Chem, except for WETD. At day 168, a + 30% CMI was registered in WETD and WETC> BWC> DRYD and DRYC> Chem. Conclusion This pattern was related to a generally marked δ13C depletion being confirmed by Δ13C, thus indicating the conservation of the carbon form compost, this very likely being related to the preferential lignin accumulation.