Development of a System for Simultaneous and Continuous Measurement of Carbon Dioxide, Methane and Nitrous Oxide Fluxes from Croplands Based on the Automated Closed Chamber Method

Abstract

A system for simultaneous and continuous measurement of fluxes of three major greenhouse gases, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), from croplands was developed based on the closed chamber method. Controlled by a computer, top-lids of the chambers placed in the field closed periodically, remained closed for about 30 min, and then opened again. During the closure of the chambers, the air in the chambers was circulated by air pumps, and part of the circulated air was injected to gas analyzers. CO2 concentration was monitored with an infra-red gas analyzer, and its increasing/decreasing rate during the 1-3-min period after the chamber closure was used for the flux calculation. Concentrations of CH4 and N2O were measured with two gas chromatographs 4 times at intervals of 8.5 min. The system was tested in lysimeter fields with Gray lowland soil under various conditions, including paddy rice cultivation, upland crop cultivation and also fallow condition. Both CH4 and N2O concentrations in the chambers increased linearly or remained almost constant during the 30-min period after the chamber closure. CO2 concentration in the chambers also increased (which indicates the predominance of respiratory CO2 emission by the crops and/or soil microorganisms) or decreased (which indicates the predominance of photosynthetic CO2 uptake by the crops) linearly during the 1-3-min period after the chamber closure. These results indicated that appropriate fluxes could be estimated for all the three gases based on the gas concentration measurements with adequate time intervals, and on the linear regression analyses. The system is expected to be effective for clarifying the comprehensive dynamics of greenhouse gases in, and for estimating the total net global warming potential of croplands. Furthermore, simultaneous measurement of the fluxes of multiple gases is also effective for analyzing the mutual relationships and mechanisms of the gas fluxes. Changes in environmental factors such as increase in air temperature or decrease in light intensity during the chamber closure (generally referred to as “chamber effect”) should be taken into account as a cause of error in the flux data.