Pedosphere 20(6): 747--760, 2010
ISSN 1002-0160/CN 32-1315/P
©2010 Soil Science Society of China
Published by Elsevier B.V. and Science Press
Diffusivity models and greenhouse gases fluxes from a forest, pasture, grassland and corn field in northern Hokkaido, Japan
1 Harvard Forest, Faculty of Arts and Sciences, Harvard University, 324 North Main Street, Petersham, MA 01366-9504 (USA)
2 Laboratory of Science, Division of Environmental Resources, Graduate School of Agriculture Hokkaido University, Sapporo, Hokkaido 060-8589 (Japan)
3 Department of Geosciences, School of Environmental Sciences, Faculty of Science, Nelson Mandela Metropolitan University, P.O.Box 77000, Port Elizabeth 6031 (South Africa)
      Information on the most influential factors determining gas flux from soils is needed in predictive models for greenhouse gases emissions.We conducted an intensive soil and air sampling along a 2 000 m transect extending from a forest,pasture,grassland and corn field in Shizunai,Hokkaido (Japan),measured CO2,CH4,N2O and NO fluxes and calculated soil bulk density (ρb),air-filled porosity (fa) and total porosity (Φ).Using diffusivity models based on either fa alone or on a combination of fa and Φ,we predicted two pore space indices: the relative gas diffusion coefficient (Ds/Do) and the pore tortuosity factor (τ).The relationships between pore space indices (Ds/Do and τ) and CO2,CH4,N2O and NO fluxes were also studied.Results showed that the grassland had the highest ρb while fa and Φ were the highest in the forest.CO2,CH4,N2O and NO fluxes were the highest in the grassland while N2O dominated in the corn field.Few correlations existed between fa,Φ,ρb and gases fluxes while all models predicted that Ds/Do and τ significantly correlated with CO2 and CH4 with correlation coefficient (r) ranging from 0.20 to 0.80.Overall,diffusivity models based on fa alone gave higher Ds/Do,lower τ,and higher R2 and better explained the relationship between pore space indices (Ds/Do and τ) and gases fluxes.Inclusion of Ds/Do and τ in predictive models will improve our understanding of the dynamics of greenhouse gas fluxes from soils.Ds/Do and τ can be easily obtained by measurements of soil air and water and existing diffusivity models.
Key Words:  air-filled porosity, gas diffusion coefficient, pore space indices, pore tortuosity factor, soil bulk density
Citation: Nkongolo, N. V., Hatano, R. and Kakembo, V. 2010. Diffusivity models and greenhouse gases fluxes from a forest, pasture, grassland and corn field in northern Hokkaido, Japan. Pedosphere. 20(6): 747-760.
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