Development of a helium atmosphere soil incubation technique for direct measurement of nitrous oxide and dinitrogen fluxes during denitrification

Abstract

A technique is described in which the upper surfaces of intact soil cores are enveloped in a flowing atmosphere of He and O2 after first purging the soil and incubation vessel free from Na. This allows the independent measurement of NaO and N2 fluxes during denitrification of added or indigenous NOT-N by direct flushing to twin gas chromatographs and without recourse to acetylene blocking. Square section cores are extracted from random locations in the field and assembled without air gaps to make composite turves in the incubation vessel, thus preserving field aerobicity and orientation but allowing the spatial variability in denitrification to be accommodated. An Na-free irrigation assembly attached to each incubation vessel can be used to apply substrates during an experimental run, which is conducted in a temperature-controlled room. Use. of the technique is demonstrated with measurements of N20 and N2 efflux from a wet, fine-textured soil under grassland management amended with nitrate and glucose. Peak concentrations were registered earlier than with previously-reported incubation techniques, with the flow rate of the incubation atmosphere having a substantial influence on the NaO to N2 ratio. Inclusion of acetylene as a component of the gas flow mixture stimulated denitrification and did not block N2 production completely. Application of the technique is limited by the extent to which atmospheric N2 contamination can be reduced and ultimately by the sensitivity of the gas chromatograph. The system in its present form has a detection limit for Na from denitrification of about 50 g N ha-' d-' and is therefore most suitably applied to soils under productive agricultural management.

Carbon amendment and soil depth affect the distribution and abundance of denitrifiers in agricultural soils

“…For real-time N-loss analysis, temporal N 2 and N 2 O evolution was measured using dedicated gas chromatographs as described by Jahangir et al (2012) in an automated incubation system ( Fig. 1; Cardenas et al 2003;Scholefield et al 1997a;Scholefield et al 1997b) at Rothamsted Research, North Wyke, Devon, UK. Sampling times for microbial analysis were chosen to reflect nitrogenous emissions; therefore, sampling times changed according to the behavior in the emission signal.…”

Theoretical and practical limitations of the acetylene inhibition technique to determine total denitrification losses

“…Hauck and Melsted, 1956;Rolston et al, 1978Rolston et al, , 1982Mosier et al, 1986), (3) direct N 2 quantification by completely replacing N 2 in the soil samples with, for example, He (e.g. Scholefield et al, 1997;Butterbach-Bahl et al, 2002;Cardenas et al, 2003), and (4) mass balance approaches (e.g. Allison, 1955).…”

An improved 15N tracer approach to study denitrification and nitrogen turnover in soil incubations

“…A key advantage of this approach over previously established gas flow methods is that it greatly reduces the sensitivity against N 2 diffusion into the incubation vessels, as the magnitude of N 2 diffusion is very low compared with the background N 2 concentration used in the new method (2% v/v). In earlier studies with conventional gas‐flow‐soil‐core incubation systems without isotope‐specific N 2 measurements, N 2 diffusion into incubation vessels resulted in a high detection limit for N 2 fluxes and measurement of very low concentration of N 2 (10–50 ppmv) were highly constrained by leakage . Another advantage is the short time needed to purge the incubation vessel with an N 2 ‐reduced artificial atmosphere.…”