Nitrous Oxide Fluxes Measurement

Abstract

Accurate field measurements of the fluxes of N2O are important for reliable up-scaling and model prediction of regional and global N2O emissions. Gaseous flux chambers are the most common field measurement technique used and represent the smallest scale, sampling an area ≥1 m2. Their operating principle is simple, they can be highly sensitive, the cost can be low and field requirements small. Chamber techniques can be applied to field trials with multiple small plots. Chamber measurements are usually made weekly and rarely more frequently than once daily. Other techniques include mass balance, and micrometeorological methods. Mass balance technique is suitable for small, defined source areas, while micrometeorological methods are suitable for measuring gas emissions on large landscape scales. Eddy covariance is the preferred technique for this scale. Relaxed eddy accumulation retains the attraction of eddy covariance by providing a direct point measurement but removes the need for a fast response gas sensor by substituting it with a fast solenoid valve sampling system. Assumptions of these methods and precautions in their application are discussed in this chapter. For N2O flux, spatially extensive and continuous measurements from agroecosystems are required, but number and frequency of measurements needed makes this difficult to achieve. Use of robust simulation models that incorporate all major regulatory processes to estimate the emissions can be the alternative of field measurements.