SOIL MESOFAUNA AND MACROFAUNA IN 2 AGRICULTURAL SYSTEMS - FACTORS AFFECTING POPULATION-DYNAMICS AND EVALUATION OF THEIR ROLE IN CARBON AND NITROGEN DYNAMICS

Data on soil meso- and macrofauna from winter wheat fields in the Netherlands under conventional and integrated management were analysed to explain their population dynamics and to evaluate their contribution to carbon and nitrogen dynamics. To compare the functioning of the soil fauna in both systems, respiration and mineralisation were calculated on a daily basis, and canonical correspondence analysis was used to analyse the response of soil fauna to abiotic factors and to biotic factors of the previous sample date. Mainly because of the occurrence of earthworms, which were absent in the conventional system, soil fauna was clearly more important in the integrated system: integrated/conventional ratios of biomass and respiration were 58.43 and 6.49, respectively for soil meso- and macrofauna. An indication of a shift of bacterivorous to fungivorous fauna was found in the integrated system under the assumption that earthworms were 80% microbivorous and 20% saprophagous, but not when it was assumed that they were 100% saprophagous. It was calculated that meso- and macrofauna mineralised 3.3 kg N ha(-1) year(-1) in the conventional and 39.8 kg N ha(-1) year(-1) in the integrated system, or 4.3% and 39.4% of the total in situ mineralisation, respectively. Total faunal mineralisation was 49.1% and 86.6% of the total in situ mineralisation in conventional and integrated systems, respectively. It was found that in both systems, seasonal factors played an important role in explaining biomass dynamics and that in the course of time, the upper layer in the integrated system increased in importance. It appeared from the analyses that food relations may differ in the two systems, with probably more complicated and diverse relations occurring in the integrated system. Analysis of the results of this study in comparison with the results of a food web approach showed general agreement; the largest deviations occurred on lower trophic levels, which may be associated with the greater sensitivity of the food web approach to the accuracy of parameter estimates.