Table 1. Mean (1 standard error in parenthesis, n = 3) for total carbon (C), δ13C of biochars and soil, and the fraction of total biochar C or soil C that is labile or mineralised in the first 2 months or over 5 years. The estimated mean residence times (MRT) of biochars, and the amount of native soil organic carbon (SOC) lost via positive priming over 2.3 years, are also shown.
| Treatmentsa | Total Cb (g kg−1) | δ13Cc (‰) | Labile Cc (g kg−1 C) | Cmin2-mo (g kg−1 C) | Cmin5-yr (g kg−1 C) | MRTc (years) | Primed C2.3-yr (mg g−1 SOC) | |
|---|---|---|---|---|---|---|---|---|
| 400°C biochars | ||||||||
| Wood400 | 697.4 (4.3) | −28.36 (0.07) | 2.6 (0.5) | 2.5 (0.2) | 19.7 (0.3) | 294 (5) | 12.8 (2.2) | |
| Leaf400A | 662.8 (2.9) | −28.13 (0.07) | 6.2 (0.4) | 5.5 (0.3) | 24.8 (0.8) | 270 (10) | 18.5 (0.5) | |
| PL400 | 431.1 (6.8) | −25.18 (0.02) | 32.9 (0.8) | 32.0 (0.8) | 69.4 (1.3) | 129 (7) | 43.8 (3.1) | |
| CM400 | 175.0 (1.5) | −27.45 (0.05) | 17.3 (1.5) | 18.3 (1.3) | 72.5 (3.0) | 90 (5) | 14.7 (0.2) | |
| 550°C biochars | ||||||||
| Wood550 | 836.1 (7.6) | −28.74 (0.08) | 1.3 (0.1) | 1.4 (0.2) | 4.8 (0.6) | 1616 (252) | 5.9 (1.6) | |
| Leaf550A | 719.8 (5.3) | −28.21 (0.07) | 3.0 (0.2) | 3.3 (1.1) | 12.4 (0.9) | 572 (32) | 16.3 (4.0) | |
| PL550A | 413.2 (1.8) | −25.22 (0.12) | 6.7 (0.2) | 7.5 (0.2) | 20.5 (1.5) | 396 (57) | 14.1 (4.2) | |
| CM550A | 165.3 (2.5) | −27.71 (0.16) | 4.9 (1.1) | 4.8 (0.7) | 22.4 (1.4) | 313 (38) | 4.4 (3.3) | |
| Smectitic soil (Vertisol) | ||||||||
| Control | 4.2 (0.06) | −14.20 (0.03) | 10.6 (0.6) | 13.4 (0.4) | 96.9 (2.1) | 58 (2) | NA | |
aTreatment details are given in Methods.
bAcid washing of biochars38 did not significantly change their δ13C value (see Table S1), thus suggesting negligible presence of inorganic carbon in biochars. Similarly, inorganic C was also absent in soil3.
cLabile C content and MRT of biochar or native SOC were determined by fitting a two-pool exponential model to the pattern of cumulative % of added biochar C or native OC mineralised over 5 years3.
NA = Not applicable.