Transformation and Persistence of Biochar Carbon In Soil: Quality and Application Implications.

One major benefit of biochar soil amendment is to permanently sequestrate carbon. Though biochar carbon is relatively recalcitrant, its long-term stability in the natural soil environment is largely unknown. Laboratory incubation and field plot experiments were conducted to investigate carbon transformation and persistence of biochar following soil incorporation. Biochars derived from different feedstocks at 400^oC pyrolysis temperature were added to a sandy loam soil at 50 g/kg and incubated at 30^oC and 10% moisture content for 24 months. Samples were collected periodically and examined for organic carbon content and functional property changes using FTIR and NMR techniques.  The biochars were further applied to field plots at 40 ton/ha. Crops were grown in the plots following generally cultivation and fertilization practices. For consecutively 5 years, soils were sampled each year and analyzed for organic carbon content and characteristics. Chemical analysis indicated that 55% of the biochar carbon was mineralizable in the environment. The lab incubation and field plot results revealed that biochar carbon were stable in soil, with less than 5% mineralized over 5 years. In accompanion, there was slightly increase in carboxylic acidity of the applied biochars.