The acetylene inhibition technique to determine total denitrification (N2 + N2O) losses from soil samples: potentials and limitations
The loss of N<sub>2</sub> from intensively managed agro-ecosystems is an important part of the N budget. The monitoring of N<sub>2</sub> emissions at the field scale is impossible due to the high atmospheric background of 78%, which precludes the measurement of fluxes. The acetylene (C<sub>2</sub>H<sub>2</sub>) inhibition technique is a rather simple, albeit imperfect, method to determine N<sub>2</sub> losses from entire soil cores. Despites serious limitations it is one among very few methodological options to estimate total denitrification at high temporal resolution and on small spatial scale, with limited workload and costs involved. A laboratory system with two different detection systems (photoacoustic IR spectroscopy and gas chromatography) is presented, which allowed parallel measurements of up to 7 intact soil cores in air-tight glass tubes in a temperature controlled cabinet (adjusted to field conditions) with an automated C<sub>2</sub>H<sub>2</sub> injection. <br><br> A survey of total denitrification losses (N<sub>2</sub> + N<sub>2</sub>O) over 1.5 yr in soil from an intensively managed, cut grassland system in central Switzerland showed a lower bound loss in the range of 6 to 25 kg N ha<sup>−1</sup> yr<sup>−1</sup> (3–13% of added N), roughly 3.4 times higher than the N<sub>2</sub>O loss. <br><br> However, several drawbacks of the C<sub>2</sub>H<sub>2</sub> inhibition technique preclude a more precise determination of the total denitrification loss.