Section 3: Aeration and Gas Transport a) How would you explain air-filled porosity for clayey soils being less than sandy soils? b) Briefly discuss why the composition of soil air is as relevant as determining the air-filled porosity in assessing soil aeration. c) The air-phase O2 concentration measured in the field was found to diminish linearly from 0.0003 g cm-3 at the soil surface to 0.000257 g cm-3 at the 0.6-m depth. The soil temperature was determined to be same as the atmospheric air temperature of 25 oC. Soil core (volume = 0.64 litres) samples were collected in the top 0.6 m of a soil profile to assess the soil’s ability to promote aeration and gas transport. The average total mass of the soil sample was determined as 1.0 kg. The samples were oven dried at 105 oC for 24 hours to obtain an average dry mass of 0.85 kg. Based on the given information about the soil: i) Determine the diffusive flux of O2 through the 0.6-m soil layer based on the soil diffusion coefficient determined from the models proposed by Penman (1940), Wesseling (1962), and Aryres et al. (1972). ii) Comment on your results for the flux based on the three models.

Section 3: Aeration and Gas Transport
a) How would you explain air-filled porosity for clayey soils being less than sandy soils?
b) Briefly discuss why the composition of soil air is as relevant as determining the air-filled porosity in
assessing soil aeration.
c) The air-phase O2 concentration measured in the field was found to diminish linearly from 0.0003 g
cm-3 at the soil surface to 0.000257 g cm-3 at the 0.6-m depth. The soil temperature was determined to
be same as the atmospheric air temperature of 25 oC. Soil core (volume = 0.64 litres) samples were
collected in the top 0.6 m of a soil profile to assess the soil’s ability to promote aeration and gas
transport. The average total mass of the soil sample was determined as 1.0 kg. The samples were oven
dried at 105 oC for 24 hours to obtain an average dry mass of 0.85 kg. Based on the given information
about the soil:
i) Determine the diffusive flux of O2 through the 0.6-m soil layer based on the soil diffusion
coefficient determined from the models proposed by Penman (1940), Wesseling (1962), and
Aryres et al. (1972).
ii) Comment on your results for the flux based on the three models.