Soil aggregation and total diversity of bacteria and fungi in various tillage systems of sub-humid and semi-arid Kenya

► Reduced tillage and crop residue management affect soil microbial community composition and diversity. ► Intercropping system performed best in promoting both microbial diversities and improvement of soil structure. ► Relationships between aggregate weight diameters and microbial indices are not always positive. ► Although fungal diversity initially declined as macroaggreation increased, a positive relationship was observed in RT+CR. Stable soil aggregates and high microbial diversity are essential for efficient nutrient recycling in soil. This study evaluated effects of different arable land-use systems on soil aggregation and associated composition and total diversity of bacteria and fungi. For this purpose, 5- and 3-year-old field trials were selected, two in sub-humid (orthic Acrisols and oxidic Ferralsols) and one in semi-arid (chromic Cambisol) region in Kenya. The treatments included combinations of tillage (conventional tillage [CT] and reduced tillage [RT]), crop residue management (0 and 2tha−1 maize stover) and cropping systems (continuous maize, maize–soybean intercropping and rotation) in the sub-humid sites, and of different tillage (CT, no-till and tied-ridging) and organic fertilization management (manure and crop residue) in semi-arid Kenya. The innovativeness of this study is the research in tropical soils where the concept of aggregate hierarchy is not generally accepted yet. The results showed that aggregate mean weight diameter (MWD) at 0–15cm depths had increased from 19 to 34% under RT relative to CT management (P