Open ventilated chamber system for measurements of H2O and CO2 fluxes from the soil surface

This paper describes the design of a ventilated ‘open’ chamber system for continuous measurement of fluxes of water and carbon dioxide from the soil surface. The system consists of four units: a chamber, an air switching unit, an infrared gas analyzer and a data logger. The chamber has the shape of a rectangular ‘box’ lying on the soil surface covering a ground area of 0.68 m⁻². The wind speed through the chamber can be regulated with a fan from zero up to a maximum of about 0.9 m s⁻¹. The soil evaporation measured by the chamber showed good agreement with evaporation measured by a balance. In situ measurement of evaporation by the chamber agreed well with evaporation estimated by a physically-based soil model. The soil water content under the chamber showed good agreement with the simulated values as well as with the water content measured outside the chamber. The magnitude of soil CO₂ efflux was in good accordance with other data reported in literature. The main error with this technique was found in the measurement of the air flow through the chamber.