Table 2. Influence of biochar (made from brush at 500°C) on N2O emissions from three different soils after a preincubation period (2 weeks).
| NO3− in soil *(mg N·kg−1 soil) | Total N2O respect to NO3− in soil (μg N2O-N·mg−1 NO3−N kg−1 soil) | Fluxes of N2 and N2O calculated by the 15N gas flux method | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| N2 (μmol kg−1 soil h−1) | N2O (μmol kg−1 soil h−1) | N2O/(N2 + N2O) | |||||||||
| Soil | Control | Biochar | Control | Biochar | Mitigation (%) | Control | Biochar | Control | Biochar | Control | Biochar |
| Secanos | 14.7 | 99.1 | 2.6 | 9.1 | — | n.d. | n.d. | n.d. | 0.06 | — | — |
| Tioga | 11.8 | 14.2 | 109.4 | 43.0 | 61 | n.d. | n.d. | 1.36 | 0.11 | 1.00 | 1.00 |
| Elba | 11.7 | 48.4 | 826.9 | 353.2 | 57 | n.d. | n.d. | 12.0 | 7.8 | 1.00 | 1.00 |
*at the maximum difference in N2O flux between biochar-control. Calculated by the 15N gas flux method. Measuring the molecular ratios for N2O of 45R (45N2O/44N2O and 46R (46N2O/44N2O) allows calculation of the enrichment of the source (15XN) of the labeled N2O48. Since we know the amount of added of NO3−–15N (50 mg, 99% enrichment), we can calculate the amount of NO3−14N that was in the soil.
n.d.: not detected. According to Stevens and Laughlin48 the detection limit with this method is 7.5 g N2 ha−1 d−1 for an enclosure with a volume to surface ratio of 5:1.