The interaction between plant roots and earthworm burrows in pasture

The distribution of burrows made by earthworms entering a soil with an established root system was measured in a field experiment, using vertically inserted mini-rhizotrons. Different root distributions were established by having pure swards of one of four pasture species (Ryegrass, Chicory, White clover and Lucerne) and different quantities of roots were maintained by cutting the sward to different heights. When plant roots are present before earthworms are active in the soil, the number and distribution of earthworm burrows is affected by both the quantity of roots and the plant species. Aporrectodea caliginosa and Lumbricus rubellus have more superficial burrows, and A. longa and L. terrestris deeper burrows in the soil profile. As earthworm burrows become established, a small proportion of plant roots explore the burrows. We suggest that the interaction between plant roots is two-way, with plant roots tending to determine the distribution of earthworms burrows and some plant roots tending to follow burrows.