Population collapse of Lumbricus terrestris in conventional arable cultivations and response to straw applications

This work assessed populations of the anecic, deep burrowing earthworm Lumbricus terrestris on two recently established (3 years) and two long running (20–170 years) organic matter amended, conventionally managed arable field trials in SE England. Validated midden counts and DNA analyses were used to estimate L. terrestris populations and check species identity (>98% match, n = 10). Population estimates ranged between 0 and 1.3 L. terrestris middens per m² on conventionally (inorganic fertiliser only) managed plots. Surface wheat straw applications (p ≤ 0.05) or wastes mixed with barley straw (p ≤ 0.05) enhanced L. terrestris midden abundances. However, these were very low at <4.6 L. terrestris middens per m² and a population collapse was recorded under oat cropping. We found a residual population ranging between 0.1–3.6 L. terrestris middens per m² on the long running field trials. Further investigations are needed to identify if L. terrestris is functionally extinct at these densities.