ROLE OF EARTHWORMS IN THE N CYCLE - A FALSIFIABLE ASSESSMENT

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