Work

A comparison of chamber-based methods for measuring N2O emissions from arable soils

Year: 2025

Type: article

Abstract: • N 2 O fluxes measured with non-flow-through chamber (NFT) methods. • N 2 O fluxes measured with flow-through chamber (FT) methods. • Water vapor correction improved agreement between NFT and FT estimations. • NFT measured 7–84 % lower N 2 O emissions than FT in various conditions. • Differences in N 2 O emissions arose from chamber design and headspace mixing. Static chamber-based flux measurements with gas chromatography are commonly used to estimate nitrous oxide (N 2 O) emissions from arable soils. The LI-COR 7820 N 2 O/H 2 O (LI-7820) enables higher-frequency in situ measurements, but side-by-side comparisons with traditional methods are limited. To address this gap, we compared non-steady-state chamber methods including non-flow-through (NFT) and flow-through (FT) chamber methods under field and laboratory conditions with plant cover or bare soil. The LI-7820 was used with the LI-8200S smart chamber (FT-1: ⌀ 20 cm) and a self-built chamber (FT-2: 60 × 60 cm), and compared to differently sized NFTs (1–4: 75 × 75, 27 × 37, 60 × 60, and ⌀ 20 cm) with manual sampling with gas chromatography. Field experiments showed high RMSE for daily N 2 O fluxes within 20 days after fertilizer application between FT-1 and NFTs, particularly for maize and spring barley (183 and 214 μg N 2 O-N m −2 h −1 ), which dropped sharply after 20 days (47 and 54 μg N 2 O-N m −2 h −1 , respectively). FT-2 and NFT-3 for pastures had lower RMSE and MAE, both below 40 μg N 2 O-N m −2 h −1 . In the incubation experiment, bare soil showed smaller error values, remaining below 26 μg N 2 O-N m −2 h −1 . Significant differences were observed between the cumulative N 2 O emissions measured with NFTs and FT-1, while differences were not significant between NFT-3 and FT-2. Several factors may explain these differences. The smaller chamber dimensions of FT-1 may influence water and nitrogen distribution and constrain the capture of spatial heterogeneity, while NFTs could be affected by prolonged deployment times and in-chamber pressure changes. Furthermore, the lack of water-vapor correction in NFTs, unlike the LI-7820, contributed to discrepancies between methods. Understanding these nuances including the impact of the chamber design, is essential for enhancing the comparability of N 2 O emissions and getting closer to achieving unbiased measurements of the true flux.

Source: Agricultural and Forest Meteorology

DOI: 10.1016/j.agrformet.2025.110591