The detectability of nitrous oxide mitigation efficacy in intensively grazed pastures using a multiple-plot micrometeorological technique
Methodologies are required to verify agricultural greenhouse gas mitigation at scales relevant to farm management. Micrometeorological techniques provide a viable approach for comparing fluxes between fields receiving mitigation treatments and control fields. However, they ha...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2014-05-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/7/1169/2014/amt-7-1169-2014.pdf |
| Summary: | Methodologies are required to verify agricultural greenhouse gas
mitigation at scales relevant to farm management. Micrometeorological
techniques provide a viable approach for comparing fluxes between
fields receiving mitigation treatments and control fields. However,
they have rarely been applied to spatially verifying treatments aimed
at mitigating nitrous oxide emission from intensively grazed pastoral
systems. We deployed a micrometeorological system to compare
N<sub>2</sub>O flux among several ~1.5 ha plots in
intensively grazed dairy pasture. The sample collection and
measurement system is referred to as the Field-Scale Nitrous Oxide
Mitigation Assessment System (FS-NOMAS) and used a tuneable diode
laser absorption spectrometer to measure N<sub>2</sub>O gradients to
high precision at four locations along a 300 m transect. The
utility of the FS-NOMAS to assess mitigation efficacy depends largely
on its ability to resolve very small vertical N<sub>2</sub>O
gradients. The performance of the FS-NOMAS was assessed in this
respect in laboratory and field-based studies. The FS-NOMAS could
reliably resolve gradients of 0.039 ppb between a height of
0.5 and 1.0 m. The gradient resolution achieved
corresponded to the ability to detect an inter-plot N<sub>2</sub>O flux
difference of 26 μg N<sub>2</sub>O–N m<sup>−2</sup> h<sup>−1</sup> under the most
commonly encountered conditions of atmospheric mixing (quantified here
by a turbulent transfer coefficient), but this ranged from 11 to
59 μg N<sub>2</sub>O–N m<sup>−2</sup> h<sup>−1</sup> as the transfer coefficient
ranged between its 5th and 95th percentile. Assuming a likely value of
100 μg N<sub>2</sub>O–N m<sup>−2</sup> h<sup>−1</sup> for post-grazing
N<sub>2</sub>O fluxes from intensively grazed New Zealand dairy
pasture, the system described here would be capable of detecting
a mitigation efficacy of 26% for a single (40 min)
comparison. We demonstrate that the system has considerably greater
sensitivity to treatment effects by measuring cumulative fluxes over
extended periods. |
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| ISSN: | 1867-1381 1867-8548 |