Accurate measurements of soil CO2 efflux are extraordinary challenging due to the very properties of CO2 transport in a porous medium of soil. The most commonly used method today are chamber methods, which provide direct measurements of CO2 efflux at the soil surface, but it can not measure the soil CO2 flux continuously. In order to develop new measurement methods in soil CO2 efflux, the small solid-state CO2 sensors (GMP222), Vaisala have been used to continuously to monitor soil CO2 profiles by burying these sensors at different soil depth (Tang et al, 2003, 2005) . The soil CO2 efflux was then calculated based on a diffusivity model.However, the leaf litter layer hasn’t been taken into consideration in the models, which make the model not applicable widely. Our experiment is to test the diffusivity model method in the lab, when there soil has different moisture content and under different temperatures, and also with/without leaf litter layer. The soil core samples were collected from SERC (Smithsonia Environmental Research Center), and also USDA(United States Department of Agriculture), which are typical forest soil and typical farm soil respectively. Then the soils moisture were set to be 10%, 20%, 30%, and were put into the incubator, where the temperature were changed from 20°C to 30°C and then from 20°C to 5°C. At the same time, soil moisture and soil temperature were measured with humidity sensor ECH2O and thermistor respectively. Measurements for each sample lasted for around two weeks, during which period, water was added to keep the moisture, also CO2 flux rate were measured with the chamber method. Leaf litter layer were then added on the soil, and the same experiment ran for another two weeks. Then the soil respiration rate was calculated based on the Fick’s Law, and compared with the chamber method.
The gas well method works better when the soil moisture is low or medium but not working well when the moisture is high or with leaf presence