Effects of earthworms on biomass production, nitrogen allocation and nitrogen transfer in wheat-clover intercropping model systems

The effects of earthworms (Lumbricidae) on plant biomass production and N a llocation in model intercropping systems of winter wheat and white clover w ere evaluated in two pot experiments. Wheat and wheat-clover mixtures were grown in a low-organic loam soil, earthworms were added at densities compar able to field population densities and the experiments were terminated 48 a nd 17 d after earthworm introductions. In both experiments, earthworms sign ificantly increased the biomass and N uptake of wheat while they had genera lly no effects on clover. As a result, earthworm activity increased the pro portion of wheat biomass in the total plant biomass of the mixture. Nitroge n budgets of the experiment lasting 48 d indicated that additional N in the system made available by earthworm activity was primarily taken up by the wheat. Earthworms also affected intra-plant N allocation in wheat which had significantly higher shoot:root N ratios when earthworms were present. Whe n clover was labelled with N-15 in the experiment which lasted 17 d, endoge ic earthworms significantly reduced the amounts of N-15 excess transferred from living or decomposing clover roots to accompanying wheat plants. Earth worms assimilated small quantities of N-15 tracer from decomposing clover r oots but not from living clover roots. The results of these model experimen ts suggest that earthworms can affect the balance between intercropped cere als and legumes by altering intra- and inter-plant N allocation.