MEASUREMENT OF SOIL GASEOUS-DIFFUSION COEFFICIENTS BY A TRANSIENT-STATE METHOD WITH A TIME-DEPENDENT SURFACE CONDITION

Gaseous diffusion coefficients of soil columns and a field soil were determined by fitting a solution of the transient-state diffusion equation for a time-dependent surface condition to measured N//2 concentration profiles. The time-dependent surface condition was experimentally imposed by pumping argon at a constant rate into a chamber placed within the soil and on the soil surface. The argon and air mixture exited the chamber through several exit ports. The N//2 concentration at the soil surface and within the soil profile was determined several times within a 5-hr period after initiation of the argon flow.