Abstract:
Global warming has grown into a serious menace in the context of climate change,
especially due to anthropogenic greenhouse gas (GHG) emissions including carbon
dioxide (CO2). Soil or the terrestrial carbon pool is one of the major sources of
atmospheric CO2. Soil respiration and decomposition of organic matter are
accountable for the emissions of CO2 from the soil. Tillage activities have the
potential to suppress or enhance CO2 emissions by altering soil respiration and
organic matter decomposition. This short-term experiment was conducted in a
Japanese Andisol during the transitional period of autumn to winter and aimed (a)
to investigate the difference of CO2 flux between no-tilled and tilled soils, (b) to
evaluate the relationship between CO2 concentration, surface CO2 flux, and gas
diffusion coefficient in the soil profile. The closed-chamber method, Ozozawa-type
diffusion apparatus, and buried gas sampling tube method were used to quantify
the soil surface CO2 flux, gas diffusion coefficient, and soil CO2 concentration,
respectively. The pooled t-test was employed to test the statistical significance (α =
0.05). Tilled soil had large relative diffusion coefficient values (0.61). Diffusivity
decreased with the depth in both systems. Significantly higher surface CO2 fluxes
were observed in tilled soil than in no-tilled, in July to September. Similar fluxes
were observed in tilled and no-tilled soils in October. Tilled soil showed CO2 fluxes
significantly lower than that of no-tilled soils in November. The magnitudes of
surface CO2 flux and soil CO2 concentration decreased in both tilled and no-tilled
soils during the transitional period. Tilled soil showed higher CO2 concentrations
(1.56 g cm-3) during autumn and low CO2 concentrations (0.28 g cm-3) at the
beginning of winter compared to no-tilled soil. No-tilled soil has relatively higher
soil moisture content and higher soil temperatures compared to tilled soil during
the transitional period. Enhanced cold-air intrusion into tilled can be considered as
the reason for the relatively low temperature in the vadose zone of tilled soil.
Higher soil moisture could have led to lower gas diffusivity inside the soil profile.
Higher CO2 concentration in soil profile increased the emissions from the soil
surface. Further evaluations will be required on variations and the amplitude of CO2
emissions from the soil under various soil types and various cropping systems as
this research was conducted in bare land.
