Alternative combinations of tillage practices and crop rotations can foster earthworm density and bioturbation

Earthworms, which contribute to important soil functions, suffer from
intensive agriculture. Their response depends among other things on the
earthworm ecological group (anecic, endogeic, epigeic) and the combination
of the applied farming practices. To advice on methodological adaptations
that enhance earthworm-mediated soil functions, effects of different
practices on earthworms need to be studied in concert. We investigated the
effects of tillage intensity (conventional, reduced, no tillage) and crop
rotation diversity (simple = wheat, barley; diverse = wheat, peas, oil
seed rape) on earthworm density and community composition in a Swedish
long-term experiment. Furthermore, we calculated annual earthworm
bioturbation to quantify the effects of farming practices on earthworm
functions. Total earthworm densities did not vary between the different
tillage intensities, but were on average 58% higher in the diverse than in
the simple crop rotation. The pattern was mainly due to the response of
the most abundant endogeic earthworms, which were not affected by tillage
intensity, but were nearly two times more abundant in the diverse than in
the simple crop rotation. Densities of anecic earthworms were 17 times
higher under no tillage than conventional tillage. Anecic earthworms also
benefitted from a diversified crop rotation, but the response depended on
tillage intensity. The level of bioturbation reflected the response of
anecic earthworms, and was more than four times higher under no tillage,
549 g dw m -2 year -1, than under conventional tillage. We conclude that
highest earthworm bioturbation is best achieved with no tillage. However,
earthworm densities and potentially bioturbation can be increased also by
a diversified crop rotation, when reducing tillage intensity is not
feasible.