Hidden allies: The role of belowground soil macrofauna in sustainable cropping production in Zimbabwe

Soil biological activity is crucial for sustainable agriculture, serving as a key indicator of soil health by regulating nutrient cycling and organic matter decomposition, and by improving soil structure. Evidence remains limited on how cropping systems, fertilizer application, and soil texture interact to structure soil macrofauna communities and modulate their functions in sub-Saharan African (SSA) maize-based agroecosystems. We evaluated the effects of fertilizer application and crop diversification strategies on soil macrofauna functionality under conservation agriculture (CA) in Zimbabwe, using field trials on variable soil textures during the 2021/22 and 2022/23 crop growing seasons. Treatments included increasing cropping system complexity: maize monoculture, maize rotations with pigeonpea or cowpea, maize-pigeonpea intercropping, and maize strip cropping with either cowpea or pigeonpea. Treatment plots were split into subtreatments with or without fertilizer application. Macrofauna were sampled 8 weeks after sowing in each season using soil monoliths (25 × 25 × 30 cm), and identified to coarse taxonomic groups. We compared cropping systems for abundance, functional, and diversity metrics: richness, Shannon index, and Pielou’s evenness. Nine taxa were consistently observed, with termites, earthworms, beetles, and ants dominating communities in both sites. Termites, which serve as a key trophic resource for many species, were most abundant in sandy soils (>300 m⁻²), whereas earthworms dominated fine-textured soils (~140 m⁻²). Maize-pigeonpea strip cropping showed the highest richness (4.47 taxa m-²) and Shannon diversity (H = 1.216), suggesting more balanced communities than other treatments. Fertilizer effects were taxon-specific, significantly enhancing only earthworm abundance (p = 0.0003) but not diversity metrics. Overall, maize-pigeonpea strip cropping supported a wider range of functional groups, including detritivores, predators, and ecosystem engineers. This system, combined with residue management, promises to enhance soil biodiversity in Zimbabwean smallholder CA systems, where pigeonpea and strip cropping remain underutilized.