The influence of two species of earthworm (Aporrectodea trapezoides and Aporrectoedea rosea) on the growth of wheat, barley and faba beans in three soil types in the greenhouse

In a greenhouse study, the ability of two earthworm species (Aporrectodea trapezoides and Aporrectodea rosea) to alter the rate of growth of wheat, barley and faba beans in three soils of contrasting texture (sandy loam, loam and clay) was examined. Three experiments are reported. In experiment 1, A. trapezoides (1, 3 or 6 per pot of 1 kg soil) in the sandy loan was associated with a significant increase in the growth (31%) of wheat seedlings at 7 weeks old, but had no significant effect in the loam or clay soils. The presence of earthworms was associated with increased foliar N concentrations (10–20%) and water-use efficiency (4–17%) in all three soil types. In experiment 2, there were no significant effects of A. trapezoides or A. rosea (10 per pot of 4 kg soil) on the dry weight of faba beans at 10 weeks old, except for A. rosea in the loam soil which reduced the total dry weight by 17%. In experiment 3, both A. trapezoides and a. rosea (10 per pot of 4 kg soil) caused a significant increase in the dry weight of barley plants (60%), root growth (40% and 30%, respectively) the number of tillers (50% and 35%, respectively) and grain yields (50% and 45%, respectively) in the sandy loam soil but had no effect on these measures in the loam soil. In the clay soil the presence of both earthworm species was associated with a substantially reduced plant dry weight (40% and 20%, respectively), tiller number (20%) and grain yield (40% and 20%, respectively). A further treatment (NPK fertiliser applied at a rate commonly used in the field) produced no increase in growth of faba beans or wheat. Effects on soil hardness and bulk density varied with soil type and earthworm species. We conclude that the response of plants to earthworm activity varied with soil type and plant species.