2.6. Monitoring of CO2 and kinetic modelling
During the incubation tests, CO2 production from untreated and
treated soil with CES, CWES and ES was quantified. A trap with
20 mL of 0.5 M NaOH was placed in each mason jar to capture CO2
flux during incubation tests. Until the 60th day of incubation, the
jars were opened every two days to maintain aerobic conditions by
exposing them for 5e10 min to ambient atmosphere. From there
on, flasks were opened once aweek. Whenever jars were opened: i)
the CO2 trapwas removed and the residual NaOH thereinwas backtitrated
with 0.5 M HCl, using phenolphthalein as indicator (BaCl2
in excess was added for precipitation of carbonates); ii) moisture of
soil samples was maintained at 65% of WHC by gravimetric
adjustment with deionized water; iii) before closing each incubation
flask, a trap with fresh NaOH was inserted. Consumption of
NaOH in each monitoring interval was stoichiometrically converted
into CO2 (Pardo et al., 2011), and the CO2 emissionwas expressed in
terms of mg CO2eC 100 g1
soil air dried d1.
Kinetic parameters describing CO2 release during incubation
were calculated by fitting the cumulative CO2eC profile to two kinetic
models (Bernal et al.,1998; Fernandez et al., 2007): first order-
E model (Eq. (2)) and parallel first order model (Eq. (3)).