Recovery and composition of biochar after feeding to cattle

Summary

To address the urgent need to mitigate agricultural greenhouse gas emissions, research is investigating innovative strategies, including the application of biochar in various agricultural practices. Feeding biochar to cattle is an interesting strategy that not only aims to improve animal health and productivity, but can also have a cascading effect on soil improvement and ­CO2 sequestration. Analysing the recovery efficiency of digested biochar and its structural integrity can provide insight into the potential of post-digestion biochar application. Here biochar quantification in dung is investigated for the first time using three different methodologies, namely thermal analysis, elemental analysis, and dichromate oxidation. Results indicate that a relative quantification within±1% biochar is possible. The majority of biochar (70–90%) fed to dairy cows survived digestion. The analysis further reveals selective preservation of the most stable condensed aromatic fractions of biochar during digestion, similar to short-term ageing 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 findings suggest that the digested biochar is highly suitable for long-term carbon sequestration when applied to soil via manure, offering a promising strategy for compensating agricultural greenhouse gas emissions.