Population dynamics in the belowground food webs in two different agricultural systems

The biomass of 17 different groups of organisms was established every 6 weeks during 1 year in two arable fields cropped to winter wheat; one field was under conventional management (CONV) and the other under integrated management (INT). Bacteria showed the highest average biomass, followed by earthworms (INT only) and amoebae. Most of the groups of organisms had higher biomasses in INT than in CONV. The difference was statistically significant for protozoans, bacterivorous, fungivorous, and phytophagous nematodes and earthworms. Predatory Collembola, cryptostigmatic and bacterivorous mites, and enchytraeids showed a smaller biomass in INT than in CONV. The annual biomass production for each group was estimated using simulation model calculations. Bacteria showed the highest production followed by amoebae and earthworms (INT only). Most of the groups showed a higher biomass production in INT than in CONV. Exceptions were predatory and nematophagous mites, predatory and omnivorous Collembola, and enchytraeids. The total annual production was approximately 32 kg C ha−1 cm−1 depth in CONV and approximately 57 kg C in INT. The population dynamics were analysed by hierarchical cluster analysis. Four different clusters were found in CONV and INT. Bacteria, fungi, protozoans, bacterivorous nematodes and predatory mites showed the same trend in population dynamics in CONV and INT. All other groups showed different population dynamics in CONV and INT. This observation and the composition of these clusters suggested different conditions in CONV and INT.