Comparison of slant open-path flux gradient and static closed chamber techniques to measure soil N 2 O emissions
Abstract. Improving direct field measurement techniques to quantify gas emissions
from cropped agricultural fields is challenging. We compared nitrous oxide
( N2O ) emissions measured with static closed chambers to those from a
newly developed aerodynamic flux gradient (FG) approach. Measurements were
made at a vegetable farm following chicken manure application. The FG
calculations were made with a single open-path Fourier transform infrared
(OP-FTIR) spectrometer (height of 1.45 m) deployed in a slant-path
configuration, sequentially aimed at retro reflectors at heights of 0.8 and
1.8 m above ground. Hourly emissions were measured with the FG technique, but
once a day between 10:00 and 13:00 with chambers. We compared the concurrent
emission ratios (FG ∕ chamber) of these two techniques and found
 N2O emission rates from a celery crop farm measured at midday by FG were
statistically higher (1.22–1.40 times) than those from the chambers
measured at the same time. Our results suggest the OP-FTIR slant-path FG
configuration worked well in this study: it was sufficiently sensitive to
detect the N2O gradients over our site, giving high temporal resolution
 N2O emissions corresponding to a large measurement footprint.