Spatial variation in soil compaction, and the burrowing activity of the earthworm Aporrectodea caliginosa

The effects of soil compaction on earthworm (Aporrectodea caliginosa nocturna) activity were studied using pot experiments. Two compaction pressures were used when packing the pots; loose soil was packed by applying a pressure of 96 kPa, and compact soil was packed using a compaction pressure of 386 kPa. "Split pots" which contained both loose and compact soil were also used. In split pots peripheral burrows (those next to the pot wall), were generally longer in the loose half of the pot than they were in the compact half. This implies that earthworms preferred the loose soil. An important finding was that peripheral burrows in the split pots were longer than those made in pots packed uniformly with either loose or compact soil. Our data suggest that the increase in activity in split pots is a response to spatial variation in soil compaction. In the split pots the earthworms tended to avoid the compact half, and we discuss how the avoidance response in the split pots may have increased the proportion of burrows in these pots that were peripheral.