| dc.description.abstract |
On a permanent pasture near Adelaide, South Australia, the amount of soil which earthworms bring to the surface each year is equivalent to a layer 0.2 mm in thickness. Although this rate of transport is too small to counteract compaction caused by livestock, it is sufficient to bury stones and other particles too large for the worms to ingest to a depth of several centimetres within a period of a few hundred years. Worm tunnels which are fresh enough to be recognized are too wide to conduct water at the tensions commonly encountered during infiltration. Even if all the tunnels are filled with air, they do not occupy enough space within the B horizon of a red-brown earth to have much influence on the rate of gaseous diffusion: at a depth of 50 cm the total cross-sectional area of the tunnels is only 0.7 sq. cm per sq. metre of soil. The space occupied by the tunnels within the A horizon is difficult to determine because of the abundance of plant roots, which are probably far more important than worms in modifying pore size distribution. |
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