Assessing the performance of the photo‐acoustic infrared gas monitor for measuring CO 2 , N 2 O , and CH 4 fluxes in two major cereal rotations

Rapid, precise, and globally comparable methods for monitoring greenhouse gas ( GHG ) fluxes are required for accurate GHG inventories from different cropping systems and management practices. Manual gas sampling followed by gas chromatography ( GC ) is widely used for measuring GHG fluxes in agricultural fields, but is laborious and time‐consuming. The photo‐acoustic infrared gas monitoring system ( PAS ) with on‐line gas sampling is an attractive option, although it has not been evaluated for measuring GHG fluxes in cereals in general and rice in particular. We compared N 2 O , CO 2 , and CH 4 fluxes measured by GC and PAS from agricultural fields under the rice–wheat and maize–wheat systems during the wheat (winter), and maize/rice (monsoon) seasons in Haryana, India. All the PAS readings were corrected for baseline drifts over time and PAS ‐ CH 4 (PCH 4 ) readings in flooded rice were corrected for water vapor interferences. The PCH 4 readings in ambient air increased by 2.3 ppm for every 1000 mg cm −3 increase in water vapor. The daily CO 2 , N 2 O , and CH 4 fluxes measured by GC and PAS from the same chamber were not different in 93–98% of all the measurements made but the PAS exhibited greater precision for estimates of CO 2 and N 2 O fluxes in wheat and maize, and lower precision for CH 4 flux in rice, than GC . The seasonal GC ‐ and PAS ‐N 2 O (PN 2 O) fluxes in wheat and maize were not different but the PAS‐CO 2 ( PCO 2 ) flux in wheat was 14–39% higher than that of GC . In flooded rice, the seasonal PCH 4 and PN 2 O fluxes across N levels were higher than those of GC ‐ CH 4 and GC ‐N 2 O fluxes by about 2‐ and 4fold, respectively. The PAS (i) proved to be a suitable alternative to GC for N 2 O and CO 2 flux measurements in wheat, and (ii) showed potential for obtaining accurate measurements of CH 4 fluxes in flooded rice after making correction for changes in humidity.