AUTOMATED SOIL MONOLITH-FLUX CHAMBER SYSTEM FOR THE STUDY OF TRACE GAS FLUXES

Soils are the major source of atmospheric N2O, and better estimates of fluxes are needed to improve the input to climatic general circulatio n models, We developed a system in a semicontrolled environment to inv estigate relationships between fluxes of N2O and controlling variables . It consists of 12 soil monoliths (1-m diam., approximate to 0.6 m de ep) in glass fiber casings, the tops of which have been converted into gas flux chambers. These chambers are connected to a gas chromatograp h for measurement of N2O and CO2. Gas sampling and analysis is compute r controlled and can be done continuously, Temperatures and soil water potential are also recorded continuously. The system has performed re liably since continuous operation began in September 1993. We conducte d three experiments, examining the effects of soil water potential, or ganic matter input, and diurnal temperature variation on N2O fluxes, t o illustrate the capabilities of the system, In these experiments, the major emissions of N2O (>800 mu g N2O-N m(-2) h(-1)) occurred when th e water potential was above -5 kPa, When plant material was incorporat ed into the soil, a highly significant correlation was found between N 2O and CO2 emissions; the N2O emissions showed pronounced diurnal cycl es, with the maxima occurring at night, 4 h after the temperature maxi ma at 0.1-m depth, Data interpretation was greatly aided by the freque ncy and continuity of measurement.