Responses of Biopore Channels from Roots to Compression by Vertical Stresses
- P. S. Blackwell ,
- T. W. Green and
- W. K. Mason
Western Australian Dep. of Agriculture, Div. of Resource Management, Geraldton, WA 6530, Australia
CSIRO Div. of soils, GPO 639, ACT 2601, Canberra City, Australia
Victorian Dep. of Agriculture and Rural Affairs, Animal and Irrigated Pastures Research Inst., Kyabram, RMB 3010, Victoria 3620, Australia
The channels created in soil by roots and soil animals (biopores) play an important role in the subsequent movement of water, air, and new roots through irrigated clay soils in southeastern Australia. The maintenance of these biopores is critical for both crop productivity and erosion control. If these biopores are to remain open, they must be able to withstand the vertical stresses associated with vehicle and animal traffic. This study had three aims: (i) to examine the influence on porosity and permeability of naturally occurring channels, (ii) to determine the magnitude of vertical stresses that artificially created channels could withstand, (iii) to test the effect of channel angle to the direction of the stress. Air-filled porosity of soil cores at −10 J/kg was decreased in a linear fashion as the applied stress was increased from 50 to 400 kPa. The reduction in air-filled porosity was relatively independent of the size or the presence of biopores. However, the intrinsic permeability of the soil cores to air was positively correlated with the diameter of the biopores, and the permeability was little affected by applied stresses up to 200 kPa if the initial diameter of the biopores was >3.5 mm. The resistance of the channels to stresses was greatest if the vertical stress was parallel to the axis of the channels. Agricultural practices on these soils should not only encourage formation of biopores, but should also minimize stresses >200 kPa to the subsoil so that these biopores can remain open.
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