Contribution of earthworms to carbon and nitrogen cycling in agro-ecosystems.

Earthworms contribute to N mineralisation directly, through consumption, digestion, respiration/ excretion and indirectly, by influencing population dynamics of other soil biota through predation or through affecting their environmental conditions. A comparison between a high-input conventional farming system with a reduced-input integrated system showed that earthworms had not colonized the conventional fields. Two methods were used to estimate the contribution of earthworms to N mineralisation in the integrated field. In the first method, the direct contribution of earthworms to N mineralisation is derived from feeding rates based on energy conversion efficiencies, life-history parameters and C:N ratios. This method also allowed the estimation of the indirect contribution, by assuming that the feeding of earthworms on their prey stimulates the growth rates of their prey. The second method calculated the amounts of mineral N derived from two sources: dead biomass and excretion products. Application of these two methods on several agro-ecosystems showed that earthworms may make a considerable contribution to N mineralisation. A sensitivity analysis, however, showed that the outcome of both methods depends on parameter estimates that are frequently uncertain. This implies that more detailed investigations on these parameters are required before the role of earthworms in energy and nutrient cycling can be established more reliably