The Effect of Direct Drilling and Minimal Cultivation on Earthworm Populations

(1) Earthworm populations in direct drilled and ploughed plots were assessed twice annually for 5 years in a continuous cereal experiment at Woburn. (2) In two other experiments, on continuous cereals at Rothamsted and Boxworth, populations of earthworms were assessed twice annually from the fourth to eighth years of cropping. The cultivations compared were deep ploughing, chisel ploughing and direct drilling. (3) Populations of the deep burrowing earthworms Lumbricus terrestris and Allolobophora longa became much greater in direct drilled than in ploughed plots and, after 8 years of direct drilling, were 17.5 and 37.3 times more numerous than in ploughed plots, at Boxworth and Rothamsted, respectively. Populations of deep burrowing species in chisel ploughed plots were intermediate between those in direct drilled and ploughed plots. By contrast, differences between populations of the shallow working earthworms A. caliginosa and A. chlorotica were much less, the greatest increase in direct drilled plots over ploughed ones being 3.4 times. (4) A survey on Lee Farm in Sussex, of earthworm populations in seven fields that had been direct drilled with cereals for several years and seven fields that had been ploughed and sown with cereals, showed significant differences in populations of L. terrestris and A. longa between ploughed and direct drilled fields but not of A. chlorotica or A. caliginosa. (5) There were significant negative correlations between populations of L. terrestris and A. longa and between those of A. chlorotica and A. caliginosa in the survey.