Regeneration of compacted soil aggregates by earthworm activity

Soil compaction is a problem of modern agriculture, caused by heavy machine ry when used in unsuitable, especially moist, conditions. Some regeneration processes in compacted loess soil were studied in a field experiment near Relliehausen, at the edge of the Selling mountains in Lower Saxony, Germany . Conventional tillage (CT) and conservation tillage (CS) systems were comp ared. The compaction was induced by the use of different wheel loads. The i nfluence of earthworms was determined by comparing soil aggregates and cast s with respect to dry and moist porosity, swelling, and water stable aggreg ation. For visualisation of the microstructure, a scanning electron microsc ope was used. The casts were obtained from two earthworm species living for 6 months in the laboratory in monoliths, taken on the plots after the whee ling procedure. The casts showed 10-20% higher values for porosity and abou t 50% higher swelling values than comparable soil aggregates, while the rel ative water stability was ca. 10% lower. We conclude that casts are looser and less stable than aggregates from the soil the earthworms ingested. To s how the ecological relevance of the changes in the casts, the cast producti on per hectare per year was calculated. It was especially high in the most loaded soil under CS with endogeic species.