Effect of temperature on biochar priming effects and its stability in soils

• Published in: Soil biology & biochemistry 2015-01, Vol.80, p.136-145
• Main Authors: Fang, Yunying, Singh, Balwant, Singh, Bhupinder Pal
• Format: Article
• Language: English
• Subjects: Biochar carbon stability; Biochar priming effect; Carbon mineralisation; Carbon stability; Temperature
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/j.soilbio.2014.10.006

Recent studies have shown both increased (positive priming) and decreased (negative priming) mineralisation of native soil organic carbon (SOC) with biochar addition. However, there is only limited understanding of biochar priming effects and its C mineralisation in contrasting soils at different temperatures, particularly over a longer period. To address this knowledge gap, two wood biochars (450 and 550 °C; δ13C −36.4‰) were incubated in four soils (Inceptisol, Entisol, Oxisol and Vertisol; δ13C −17.3 to −28.2‰) at 20, 40 and 60 °C in the laboratory. The proportions of biochar- and soil-derived CO2–C were quantified using a two-pool C-isotopic model. Both biochars caused mainly positive priming of native SOC (up to +47 mg CO2–C g−1 SOC) in the Inceptisol and negative priming (up to −22 mg CO2–C g−1 SOC) in the other soils, which increased with increasing temperature from 20 to 40 °C. In general, positive or no priming occurred during the first few months, which remained positive in the Inceptisol, but shifted to negative priming with time in the other soils. The 550 °C biochar (cf. 450 °C) caused smaller positive priming in the Inceptisol or greater negative priming in the Entisol, Oxisol and Vertisol at 20 and 40 °C. At 60 °C, biochar caused positive priming of native SOC only in the first 6 months in the Inceptisol. Whereas, in the other soils, the native SOC mineralisation was increased (Entisol and Oxisol) and decreased (Vertisol) only after 6 months, relative to the control. At 20 °C, the mean residence time (MRT) of 450 °C and 550 °C biochars in the four soils ranged from 341 to 454 and 732−1061 years, respectively. At 40 and 60 °C, the MRT of both 450 °C biochar (25−134 years) and 550 °C biochar (93−451 years) decreased substantially across the four soils. Our results show that biochar causes positive priming in the clay-poor soil (Inceptisol) and negative priming in the clay-rich soils, particularly with biochar ageing at a higher incubation temperature (e.g. 40 °C) and for a high-temperature (550 °C) biochar. Furthermore, the 550 °C wood biochar has been shown to persist in soil over a century or more even at elevated temperatures (40 or 60 °C). •We measured C mineralisation in biochar amended soils for a two-year period.•Biochar increased the mineralisation of native organic carbon in a sandy soil.•In clayey soils, biochar suppressed the mineralisation of native organic carbon.•Biochar-C mineralisation decreased with increasing pyrolysis temper