Toward an assessment of multiple soil taxa and their interactions in alternative and transitioning cropping systems

Developing cropping systems that promote soil biodiversity is crucial to guarantee sustainable production in the face of global changes. However, effects of alternative systems on soil organisms remain largely unknown. For two consecutive years, soil microorganisms, mesofauna and macrofauna were collected in 21 fields under conventional, organic or conservation agriculture, either long-established or transitioning, ranging in tillage intensity, pesticide treatment intensity and organic inputs. Effect sizes were calculated to compare taxa density or diversity between alternative and conventional systems, and between transitioning and long-established systems. Piecewise structural equation modeling was conducted to assess relations between practices and soil trophic groups. Long-established conservation systems had positive effects on various taxa densities (Collembola, Coleoptera larvae, Gastropoda) and earthworm biomass, but negative effects on fungal richness. Recent conservation systems had positive effects on Coleoptera larvae density, earthworm density and biomass, and negative effects on fungal abundance (10–20 cm depth). Recent organic systems benefited earthworm density and biomass, and fungal diversity. Transitions from conservation to organic decreased Araneae density and influenced microbial and Collembola diversity. Conservation, and to a lesser extent organic systems, had overall positive effects on soil organism density. Tillage intensity showed the strongest negative effect on soil organisms with cascading effects through the soil food web, while organic matter inputs promoted bacteria and macrofauna detritivore densities. Mesofauna detritivores played a central role in studied soil food webs. Overall, conservation and organic agriculture benefit different taxa, and reduced tillage could offer the greatest benefits by promoting soil taxa and their interactions. • Cropping system and practice intensity effects on soil organisms and interactions. • Conservation and organic systems, even in transition, benefited different soil taxa. • Conservation and organic systems had a positive overall effect on soil organisms. • Tillage intensity has a strong negative effect on soil organisms and soil food web. • Mesofauna detritivores play a central role in agroecosystem soil food webs.