Effect of introducing earthworms into horticultural land previously denuded of earthworms

Abstract

An intensive vegetable growing area with no resident earthworms has received, since 1984, three cultivation treatments, involving varying degrees of disturbance, and two cropping regimes, a summer and winter crop with a winter ryegrass cover crop. Five species of Lumbricidae were introduced to part of each treatment in 1986 to assess the effect of cultivation treatments on earthworm establishment and survival, and the effect of earthworms on some soil characteristics. The experiment was designed so the effects of earthworms could be interpreted against the background of periodic changes in soil characteristics caused by cultivation, crop species and weather. Earthworm population density (numbers m −2) and activity (casts m −2) decreased with increasing intensity of cultivation. Cellulose decomposition rates were increased up to 30% by the presence of earthworms, although cultivation per se had no apparent effect. By contrast, cultivation substantially reduced soil strength (measured by impact penetrometer) while earthworm introduction had no significant effect. Similarly, saturated hydraulic conductivity of the topsoil (measured in situ) appeared unaffected by earthworms. However, infiltration and air-permeability measurements indicated that earthworms had improved the structure of the bulk soil matrix.