Amending soil with biochar (pyrolized biomass) is suggested as a globally applicableapproach to address climate change and soil degradation by carbon sequestration, reducingsoil-borne greenhouse-gas emissions and increasing soil nutrient retention. Biochar wasshown to promote plant growth, especially when combined with nutrient-rich organic matter,e.g., co-composted biochar. Plant growth promotion was explained by slow release ofnutrients, although a mechanistic understanding of nutrient storage in biochar is missing.Here we identify a complex, nutrient-rich organic coating on co-composted biochar thatcovers the outer and inner (pore) surfaces of biochar particles using high-resolution spectro(micro)scopy and mass spectrometry. Fast field cycling nuclear magnetic resonance, electrochemicalanalysis and gas adsorption demonstrated that this coating adds hydrophilicity,redox-active moieties, and additional mesoporosity, which strengthens biocharwaterinteractions and thus enhances nutrient retention. This implies that the functioningof biochar in soil is determined by the formation of an organic coating, rather than biocharsurface oxidation, as previously suggested.
- Advanced Materials Science
- Basic - Fundamental (Grundlagenforschung)