A recent article in the scholalry journal Soil Biology and Biochemistry provides more evidence to the significant longevity of solid carbon in agricultural soils. Researchers Yakov Kuzyakov, Irina Subbotina, Haiqing Chen, Irina Bogomolova and Xingliang Xu at the University of Bayreuth produced biochar samples from perennial ryegrass. These samples were labeled with a radioactive carbon isotope and mixed into soil samples. Soil samples were allowed to incubate for 3.2 years, and were subjected to various treatments intended to stimulate the decomposition of biochar. Despite these treatments, which included addition of glucose and intensive mixing of soils, biochar was not found to contribute significantly to overall carbon flux, indicating minimal leaching and degradation of black carbon in agricultural soils. Based on their experiments, the researchers conclude that black carbon has a half-life of at least 1400 years, and a mean residence time of at least 2000 years in agricultural soils. Given the relatively short duration of their experiment, the researchers postulate that this residence time could be even longer.
For the biochar community, this news is potentially huge. One of the strongest criticisms of biochar has been the lack of multi-year soil studies. Given the relative novelty of the biochar concept, this long-standing review will only support biochar in the face of increasing challenges.