Earthworms generally exert beneficial effects on plant growth. However, negative effects may be induced under particular situations. The effect on grain yields is also proportional to the earthworm biomass; significant effects start to appear at biomass values> 30 g fresh weight (Brown et al ., 1999), although very high biomasses of single species of earthworms, (. Pontoscolex corethrurus ) may inhibit production under particular situations. Many mechanisms are involved in the growth stimulation. These vary from large-scale effects on soil structure and nutrient availability, to the enhancement of mycorrhizal infection or control of plant-parasitic nematodes. Once the earthworms are established, a dynamic cropping system - involving crop rotations with long cycle crops or perennials with good organic matter additions - contributes to securing long-lasting benefits from earthworm activities.