Abstract:The aim of this study was to investigate the influence of pyrolysis temperature on the physic-chemical properties of biochar, and the effect of biochar addition on carbon contents of soil organic matter fractions and carbon mineralization characteristics. Biochars were produced by fast pyrolysis of apple tree twigs at 300, 400, 500 and 600℃, respectively. Characterizations of biochars were determined by elemental analysis, Brunauer—Emmett—Teller (BET) for surface area, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy. Four kinds of biochar were added to soils at five application rates as soil only (control), soil+0.5% biochar, soil+1% biochar, soil+2% biochar and soil+3% biochar, which were incubated at 25℃ in lab. Carbon mineralization was analyzed by alkali absorption of CO2 released periodically over 180d. Soil samples were analyzed for microbial biomass carbon (MBC) and soil dissolved organic carbon (DOC). The results showed that the generated biochars contained 62.20%~80.01% of carbon (C), 2.72%~5.18% of hydrogen (H) and 15.99%~30.94% of oxygen (O). The BET surface area was 2.35~107.76m2/g, basic functional groups were 0.11~0.40mmol/g and acidic functional groups were 0.44~1.16mmol/g. The increasing temperature (from 300℃ to 600℃) increased biochar C content, BET surface area and basic functional groups, while decreased the content of O and H, H/C and O/C ratio, acidic functional groups and total functional groups. Soil respiration, MBC and DOC were increased by biochar application. As pyrolysis temperature increased and biochar application rate decreased, soil respiration, MBC and DOC decreased in all soils. The mineralization of biochar C decreased significantly (P＜005) from 7.86% to 0.60% when pyrolysis temperature increased from 300℃ to 600℃. A doubleexponential equation was used to describe C mineralization kinetics and curve fitting was performed to mathematically define the size and turnover rate of two C source pools (labile and stable). The size of labile pool (A1) varied from 0.31g/kg to 0.94g/kg, while the size of stable pool (A2) varied from 6.88g/kg to 30.82g/kg. The decreased mineralization rates of the labile and stable pools (k1 and k2) were resulted from the increased pyrolysis temperature and the decreased biochar application rates. Halflife of C in soil varied between 24.09a and 44.76a and increased with the increase of pyrolysis temperature and biochar application rates. Conclusively, pyrolysis temperature had important effect on the physico-chemical properties of biochar and therefore resulting in different stabilities of soil organic matter. Considering the carbon loss in the process of preparing biochar, 500℃ would be the optimal temperature for preparing apple-derived biochar due to the most significant promotion of soil organic carbon.
