Location-dependency of earthworm response to reduced tillage on sandy soil

Since earthworms are of functional importance in soils, understanding their sensitivity to tillage is of importance for the design of sustainable management systems. The effect of reduced, ploughless tillage on earthworm abundance was explored during a 10-year observational study on a producer’s field on sandy soil. The analysis of tillage effects is complicated by the fact that earthworms are not only affected by tillage but also by soil properties. We analyzed the spatial distribution pattern of earthworms (Lumbricidae) in a heterogeneous 74 ha field in Northeast Brandenburg, Germany. Earthworm populations were assessed by means of handsorting along 4 transects on 42 permanent plots which were partly under conventional, partly under reduced tillage. Different earthworm activity parameters were calculated for each plot and related to soil properties such as soil texture and organic carbon in 0 to 15 cm. In addition, paired plots were analyzed at both sides of the dividing line between the tillage systems. The analysis of paired plots indicated that finer textured soils react more positively to tillage reduction than sandy soils. State-space analysis confirmed that soil texture was important in all cases for estimating earthworm parameters along the transects. Organic carbon in 0 to 15 cm, indicative of the tillage system, was an especially important predictor for maximal abundances of earthworms in the year 2000. Our observations also suggest higher spatial variability of earthworm abundances and closer relationships between earthworms and soil texture under reduced tillage. For separating soil from management effects in landscape scale studies, approaches are promising which take into account the spatial variability of soil properties and soil biota.