Does feeding biochar to cattle impair its carbon sequestration efficiency?

To address the urgent need to reduce greenhouse gas emissions from agriculture and to promote soil carbon sequestration, innovative approaches such as the incorporation of biochar into different agricultural practices are needed. Feeding biochar to cattle is an interesting strategy that not only aims to improve animal health and productivity, but may also have a cascading effect on soil improvement and CO2 sequestration, thereby addressing different facets of modern agriculture. Analysis of the recovery efficiency of digested biochar and its structural integrity can provide insight into the potential for post-digestion biochar applications. Here, a controlled feeding trial¹ with dairy cows and a 1% biochar supplement in the diet was conducted and biochar recovery and composition in manure was analysed. Quantification of biochar in manure was investigated for the first time using methods based on thermal analysis, elemental analysis and dichromate oxidation, and shows that relative quantification of biochar is possible to within ± 1%. Overall, the majority of biochar (70-90%) fed to dairy cows survived digestion. The analysis also indicated selective preservation of the most stable condensed aromatic fractions of biochar during digestion, similar to short-term aging in soil. The remaining digested biochar has an H/C ratio of 0.22 and an O/C ratio of 0.05, meeting the criteria for highly stable biochar. Our results suggest that the digested biochar is highly suitable for long-term carbon sequestration when applied to soil via manure, offering a promising and economically viable strategy for carbon farming.

Reference

1 Dittmann et al., Animal Feed Science and Technology 318 (2024) 116127