Carbon stability and biochar aging process after soil application.

Abstract: During the pyrolysis process for biochar production there is the stabilization of C in aromatic compounds, which accredits biochar to function as an input for C sequestration in the soil. The aim of this study was assessing of C sequestration potential through pyrolyzed biochar in low temperature (350-400oC), checking the possible deleterious effect in soil organic matter (SOM) and assessing the cation exchange capacity (CEC) alteration, as the biochar is aging.The research strategy involved, besides the materials characterization, the installation and conduction of two incubations under controlled laboratory conditions.The evaluation of the biochar stability of C carbon, the effects on SOM and, therefore, the potential for the use of biochar in soil C sequestration was carried out in a respirometric experiment, with four typical tropical soil samples mixed with eucalyptus biochar dose (0.0, 2.5, 5.0, 10.0 and 20.0 g Ckg-1). After 120 days of incubation under non-limiting temperature and moisture conditions, the results showed C mineralization rates between 0,4 and 9,3%, which demonstrates the high carbon stability in the biochar. Through the 13C technique in soil analysis at the end of the incubation was observed small reductions of original C in SOM for two of the evaluated soils, although gains from biochar application represented more than double the original C content of soils.The 360-day incubation experiment to evaluate biochar aging, focusing on the generation of negative charges, considered the variation in the presence or absence of soil; moisture and temperature (25 or 32°C). Among the factors tested, there was only effect of time on CEC. The increase in CEC was practically 100 mmolc kg-1 in one year, which represented a 50% increase in surface charges due to the biochar aging process.The research led to the conclusion that biochar must be considered an input to soil C sequestration, in the reason of its high stability after application, recommending the use of the conservative value of 90% of the total C applied via biochar rate to environmental accounting related to C sequestration. In addition, increases in CEC in biochar treated soils are expected due to biochar surface charges as well as the aging process after application.