Intensive cultivation can drastically reduce earthworm populations in arable land

The impact of intensive cultivation for potato production on the earthworm populations was assessed in two adjacent large field plots. Three successive winter wheat crops had been grown in one plot while winter wheat was grown with minimum cultivation in an understorey of white clover in the other. Both plots were ploughed in spring 1998 and intensively cultivated (grubbing, ridging, bed-tilling, destoning, ridging) prior to planting potatoes. Earthworm populations were reduced from a mean density of 319 individuals m–2 and 55 g m–2 biomass in the conventional wheat plot, and from 1160 individuals and 175 g m–2 biomass in the wheat–clover plot in the 1996/1997 cropping season, to 40–82 individuals and 4–19 g m–2 in June–October 1998 following potato planting. Populations declined to virtually undetectable levels following mechanical potato harvesting in late autumn 1998 and spring cultivation for barley in 1999, remained at very low levels throughout 1999 and had shown no sign of recovering by May 2000. The results show that earthworm populations can be virtually eliminated within a single season by drastic forms of soil cultivation.