An improved dynamic chamber technique for measuring CO2 efflux from the surface of soil

1. A new dynamic chamber has been developed with the aim of improving the performance of existing techniques for measuring CO2 efflux from the soil surface. It has been shown that differences in the flow rates of incoming and outgoing air can be balanced quickly with this new chamber, consequently reducing the pressure difference between the inside and outside of the chamber. In the new chamber, the pressure difference varied within +/- 0.2 Pa at flow rates of up to 4 litres min(-1) when placed on the soil surface, whereas the corresponding value for an earlier design of chamber was about +/- 1.0 Pa. The improved chamber can give a better and a more reliable estimation of CO2 evolution from the soil surface compared to existing dynamic chambers, as demonstrated by either the magnitude or the trend of daily variation of measured CO2 effluxes. 2. In a dynamic chamber technique, the pressure difference depends mainly upon the flow rate of sample air and the length and diameter of inlet or outlet tubing through which air passes into or out of the chamber. It is difficult to obtain steady and negligible pressure difference with a normal dynamic chamber, especially if the method employs simultaneously blowing and drawing air, as the pressure difference is very changeable.