Impact of soil compaction on earthworm burrow systems using X-ray computed tomography: preliminary study

This study is a first approach of the impact of soil compaction due to trafficking by machinery on earthworm burrow systems. To this end, two experiments were established. In the first one, microcosms were incubated in the laboratory for 70 d with Lumbricus terrestris or Aporrectodea giardi. In the second experiment, soil cores were excavated from a sugar beet field mainly colonised by L. terrestris and Aporrectodea caliginosa. The cores were then artificially compacted at 0.12 MPa or 0.25 MPa (which corresponds to the compaction due to trafficking by machinery in the field) or remained non-compacted. The whole cores were submitted to an X-ray computed tomography scan. This method allowed to compare the characteristics of the entire burrow system (total and mean burrowed length, mean length and number of burrows) and of the burrows themselves (number, area and roundness of pores constituting the burrows) in the compacted and non-compacted cores. The results showed that soil compaction contributes to close numerous pores, reduce mean length of burrows and increase the number of fragmented burrows. We concluded that soil compaction affects to a large extent the functionality of burrow systems by fragmenting them and affecting their continuity. This impact increases with the intensity of compaction. The applied soil compaction mainly affected the burrows located in the upper part of the soil. From a general point of view and especially for the upper part of the cores, horizontal burrows seemed to be more affected by compaction than vertical or oblique ones. Globally, the effects of soil compaction were especially observed at the greatest applied pressure (0.25 MPa). At 0.12 MPa, the damage to the burrows was less obvious.