Low-power flux gradient measurements for quantifying the impact of agricultural management on nitrous oxide emissions

Nitrous oxide (N2O) emissions from agricultural soils occur as pulses presenting a challenge for assessing mitigation practices. Since the timing and magnitude of pulses is dependent on soil and climatic conditions, side-by-side comparisons are needed. The flux gradient (FG) and eddy covariance (EC) methods both capture spatially and temporally variable N2O emissions, but FG requirements are more flexible for operation using low power and/or in a multi-plot configuration with one gas analyzer. Instrumentation for N2O flux measurement requires strong pumps (> 500 W), limiting deployment. Here we developed new instrumentation using the FG method with minimal power (∼30 W). Field measurements were conducted in 2017 and 2018 in an agricultural field in Ontario, Canada to test the equipment's measurement quality, power consumption, and ease-of-use. A low-power FG system (FGLP) was co-located with an N2O EC flux tower (N2O-EC) and an existing multi-plot FG system (FGMP) was operated ∼50 m away. The FGLP fluxes correlated well with N2O-EC (r2 = 0.97, slope = 1.05), and ran uninterrupted with minimal maintenance using only 30 W. The non-co-located FGMP still showed relatively good correlation with N2O-EC (r2 = 0.65) through the growing season although there was a mismatch in measurement footprints, and N2O fluxes are well-known to occur in hot spots. Better agreement was observed for FGMP measured CO2 fluxes and the EC system (slope = 0.97, r2 = 0.93), giving additional confidence in the FGMP. The FG systems captured important N2O pulses during rainy, foggy and dewy periods when N2O-EC data was discarded. Results confirmed the functionality of the new FGLP system and verified FG measurements against EC N2O fluxes. The low power option provides possibilities to expand measurement to locations with power restrictions using a multi-plot configuration for side-by-side comparisons essential for evaluating effects of agricultural practices on N2O emissions.