11 a.m. and was always completed by 1 p.m.
The CO2 efflux rate was computed from the time course of CO2
concentration increase (slope) following the fitting of the chamber
to a collar – system volume of 991 cm3 and receiving CO2
from a known soil surface area of 79 cm2. In preliminary experiments,
it was found that multiple measurement cycles at the same
location provided highly reproducible results. This allowed a CO2
efflux measurement to be made from a single cycle of concentration
increase in each sampling location. This in turn allowed completion
of CO2 efflux sampling from all 60 locations (2 plots
×
30 locations
per plot) in minimal time (∼2 h) and so with minimal variation in
soil temperature.