Analysis of Chamber Methods Used for Measuring Nitrous Oxide Production in the Field

Abstract

Abstract Two current procedures for measuring nitrous oxide (N 2 O) production in the field are studied using a two‐dimensional model of gas production and diffusion through soil. These procedures consist of trapping the gas as it leaves the soil surface, either by allowing the gas to build up in a closed chamber (closed cover), or by removing and measuring the gas as it leaves the soil (open cover). The model calculations suggest that in many cases, neither measurement relates well to the N 2 O production rate because the gas concentration is still building up in the soil. There are also expected differences between the two methods, with the closed cover measurement underestimating the flux from the soil when air contents are relatively high while production is occurring, if gas is allowed to build up in the chamber for more than a few hours. The calculations suggest that, due to the large phase lag caused by gaseous diffusion, the only way to obtain accurate information about the extent of N 2 O release to the atmosphere from the soil from a denitrification‐reduction event is to trap all gas which is produced by the process. This may require monitoring for up to several weeks after production ceases if soil water content remains high.