TY - JOUR
T1 - Oxygen transport to plant roots
T2 - Modeling for physical understanding of soil aeration
AU - Cook, F. J.
AU - Knight, J. H.
PY - 2003
Y1 - 2003
N2 - A model that couples the diffusion of O2 to plant roots at the microscale to diffusion of O2 through the soil at the macroscale is derived. The solution is complex, but if the length scales (Zr and Zm; see APPENDIX for list of symbols) are equated a simple analytical expression can be obtained. This model is used to investigate relationship between a critical air-filled porosity (θm) and the other parameters; viz temperature (T), O2 concentration in the bulk soil (C*), O2 concentration at the root surface (Cr), root length density (L), the ratio of root radius (a) to the water film radius (R), microbial respiration (Mo), and length scales (Zm and Zr) related to the depth to which microbial and plant respiration are active in the model using sensitivity analysis. The model shows that θm is not very sensitive to the O2 concentration at the root surface (Cr), or the ratio of root radius (a)I water film radius (R), but is sensitive to all the other parameters in some part of their range. The results indicate that indices used to define soil aeration; O2 diffusion rate (ODR) or O2 flux, O2 concentration, or air-filled porosity, which have been previously used, are related and a single critical value for these is unlikely. If a constant critical value exists for one of these indexes it cannot exist for the other two. It is also shown that it is highly unlikely that a universal critical parameter related to soil aeration exists for any of these parameters. It is concluded that more parameters than ODR, O2 concentration, or air-filled porosity need to be measured if progress in soil aeration research is to be made.
AB - A model that couples the diffusion of O2 to plant roots at the microscale to diffusion of O2 through the soil at the macroscale is derived. The solution is complex, but if the length scales (Zr and Zm; see APPENDIX for list of symbols) are equated a simple analytical expression can be obtained. This model is used to investigate relationship between a critical air-filled porosity (θm) and the other parameters; viz temperature (T), O2 concentration in the bulk soil (C*), O2 concentration at the root surface (Cr), root length density (L), the ratio of root radius (a) to the water film radius (R), microbial respiration (Mo), and length scales (Zm and Zr) related to the depth to which microbial and plant respiration are active in the model using sensitivity analysis. The model shows that θm is not very sensitive to the O2 concentration at the root surface (Cr), or the ratio of root radius (a)I water film radius (R), but is sensitive to all the other parameters in some part of their range. The results indicate that indices used to define soil aeration; O2 diffusion rate (ODR) or O2 flux, O2 concentration, or air-filled porosity, which have been previously used, are related and a single critical value for these is unlikely. If a constant critical value exists for one of these indexes it cannot exist for the other two. It is also shown that it is highly unlikely that a universal critical parameter related to soil aeration exists for any of these parameters. It is concluded that more parameters than ODR, O2 concentration, or air-filled porosity need to be measured if progress in soil aeration research is to be made.
UR - http://www.scopus.com/inward/record.url?scp=0037245130&partnerID=8YFLogxK
U2 - 10.2136/sssaj2003.2000
DO - 10.2136/sssaj2003.2000
M3 - Article
SN - 0361-5995
VL - 67
SP - 20
EP - 31
JO - Soil Science Society of America Journal
JF - Soil Science Society of America Journal
IS - 1
ER -