CONTRIBUTION OF EARTHWORMS TO CARBON AND NITROGEN CYCLING IN AGROECOSYSTEMS

Earthworms contribute to N mineralisation directly, through consumptio n, digestion, respiration/excretion and indirectly, by influencing pop ulation dynamics of other soil biota through predation or through affe cting their environmental conditions. A comparison between a high-inpu t conventional farming system with a reduced-input integrated system s howed that earthworms had not colonized the conventional fields. Two m ethods were used to estimate the contribution of earthworms to N miner alisation in the integrated field. In the first method, the direct con tribution of earthworms to N mineralisation is derived from feeding ra tes based on energy conversion efficiencies, life-history parameters a nd C:N ratios. This method also allowed the estimation of the indirect contribution, by assuming that the feeding of earthworms on their pre y stimulates the growth rates of their prey. The second method calcula ted the amounts of mineral N derived from two sources: dead biomass an d excretion products. Application of these two methods on several agro -ecosystems showed that earthworms may make a considerable contributio n to N mineralisation. A sensitivity analysis, however, showed that th e outcome of both methods depends on parameter estimates that are freq uently uncertain. This implies that more detailed investigations on th ese parameters are required before the role of earthworms in energy an d nutrient cycling can be established more reliably.