Role of earthworms in the N cycle: A falsifiable assessment

Due to the great difficulty in measuring N transfers in the field, most N-cycle representations are made from laboratory data extrapolated to field earthworm populations. Nevertheless, since 1975 advances have been made and a general model has been proposed based on field transfer measures, which is applicable to various (anecic) earthworm populations. The advances were, chronologically, as follows: (1) the choice of a conceptual model with measurable compartments and possibly transfers; (2) the use of nontoxic dye for labelling earthworms; (3) the use of additional N-15 labelling in field; (4) the improvement of a mathematical model with efficient fitting to field data; (5) the adjusting of a technique to measure the earthworm gut transit in the field; (6) the field validation of predicted results; (7) the description of driving factors (photoperiod, soil temperature and moisture) of the earthworm N activity; and (8) the full description of the knowledge used in the interpretation in an Explained Knowledge Dispenser as an informatics server. This process is presented in the paper and leads to an estimate of 1.75 kg ingested N, 1.15 kg defecated N and 0.6 kg assimilated plus excreted (metabolized) N kg(-1) of live anecic earthworms y(-1) in a temperate climate. These results are falsifiable, thanks to new predictions of the model and new field observations. (C) 1997 Elsevier Science Ltd.