Miss Marie-Liesse Aubertin1, Mr Cyril Girardin2, Mrs Sabine Houot2, Mrs Cornelia Rumpel1
1CNRS, IEES, UMR 7618, CNRS‐UPMC‐UPEC‐INRA‐IRD, 78820 Thiverval‐Grignon, France, 2INRA, Ecosys, UMR INRA‐AgroParisTECH, 78820 Thiverval‐Grignon, France
Application of Biochar, a solid product produced from biomass pyrolysis under low oxygen conditions, has been suggested as a low emission technology capable of increasing soil C sequestration to mitigate climate change. Due to its low reactivity and nutrient value in the first years after its deposition, the combined application of biochar with compost may be a promising avenue to ameliorate soil quality while increasing C sequestration. We hypothesize that synergistic effects of both materials have positive effects on organic matter protection. This study aims to compare the stability of six biochar-compost mixtures differentiated by biochar type, at a short time scale. Biochars were produced from different feedstocks at 650°C for 10 minutes. Our conceptual approach included incubation of fresh and artificially aged biochar-compost mixtures. Physical ageing of the mixtures was performed with successive cycles of humidification/drying and freezing/thawing. We evaluated microbial biomass, the elemental composition and stability of the fresh and aged mixtures after incubation with a soil inoculum for 15 weeks. We monitored biochar decomposition when produced from C4 feedstock by determination of the 13C signature of emitted CO2.
Mineralization kinetics of the biochar-compost mixtures depended on the nature of biochar, with mixtures containing biochar produced from maize biomass showing faster mineralization than mixtures containing biochar from miscanthus. C:N ratio, also depending on the nature of the biochar, were directly correlated with mineralization kinetics; a growing C:N ratio induced a lower mineralization rate. C:N ratios from biochar from miscanthus biomass had a different connection with mineralization rate. Results showed that biochar ageing influenced its interaction with compost by reducing the mixtures’ decomposition rate. However, aged biochar from miscanthus feedstock more than doubled mineralization rate of the compost. We therefore conclude that biochar feedstock determines the capacity of biochars to interact with compost after ageing.