Potential for carbon sequestration after biochar-P fertilizer application: A biological and chemical assessment

Innovation is required on many fronts in agriculture, not only to improve nutrient use efficiency but also to mitigate the effects of climate change. Our previous studies presented the high agronomic efficiency of an experimental phosphate fertilizer using a biochar-matrix, called 'BioFert'. However, the efficiency of BioFert for soil carbon sequestration goals has not yet been evaluated. We incubated BioFert and initial raw sugarcane-biochar over 56 days in two soils (i.e., Ferralsol and Alisol) and measured the total CO2 and delta C-13-CO2 to quantify the contribution of native soil organic matter, sugarcane-biochar, or BioFert to carbon mineralization. There was no significant difference in cumulative CO2 release between BioFert and the control (without carbon addition), and BioFert was less mineralized than carbon from sugarcane-biochar regardless of soil type. In addition, accelerated aging by thermal oxidation of these carbon sources revealed that more than 80% of BioFert-carbon was prevented from accelerated mineralization, while sugarcane-biochar achieved similar to 80% of carbon mineralization. The residual solids after oxidation were analysed by X-ray photoelectron spectroscopy and indicated aliphatic/aromatic and carboxylic chemical bonds on the BioFert surface, which might offer new cation exchange sites over time. We conclude that BioFert is not only a phosphate fertilizer with high phosphorus use efficiency but also a stable source of carbon for soil carbon sequestration purposes.