Comparison of different monitoring and estimation methods for N₂O emissions from greenhouse vegetables production

Objectives In order to introduce an inverse dispersion technique to evaluate N₂O emissions from greenhouse with vegetable production, static box gas collection instruments with gas chromatography analysis were used simultaneously to check N₂O emission. The results were compared and analyzed to test the feasibility of this new approach.

Methods In the vegetable greenhouses of the facility, a fertilizing area and a non-fertilizing area were set up. Using box-type method and micro-meteorological method to carry out 72-hour high-frequency monitoring and full-growth monitoring, N₂O concentration characteristic curve and emission flux characteristic curve were constructed by measuring results.

Results The results showed that the N₂O concentration at 3.5 m above the shed area of the vacant period was significantly lower than that of the planting period. The nighttime concentration during the vacant period was higher, and the daytime concentration during the planting period was higher. The concentration of N₂O in the greenhouse decreased with the increase of height, and the difference of N₂O concentration between different heights was significant, which was higher than the external background concentration. The result of the N₂O daily emission characteristics by static box/gas chromatogram method and inverse dispersion technique had good consistency, but the former was generally higher than the latter. The average three-day emission flux measured by inverse dispersion technique was 192.2 μg/(m²·h). The average gas emission flux measured by static box/gas chromatogram was 252.5 μg/(m²·h). The difference was 26.8%. In both ways, the flux curve tended to be consistent across the entire growing season of the plant tomato. The cumulative emission flux measured by static box/gas chromatogram was 1817.5 g/hm², and the emission factor was 0.45%. The cumulative emission flux measured by inverse dispersion technique was 1250.95 g/hm², and the emission factor was 0.32%, which was 29% lower than that measured by the static box method.

Conclusions The results of the inversion gas diffusion model and the static box/gas chromatography method on the N₂O flux in the vegetable field planting area have good consistency. But the results of the inverse dispersion technique are significantly lower than those of the static box/gas chromatogram method. However, the inversion gas diffusion model has a high degree of automation, which can monitor the whole process of N₂O emission in the vegetable field with high density and is suitable for observation in a large area. It provides a reference for the existing measurement methods and provides new ideas for establishing a diversified N₂O emission monitoring system.