How Does No-till Affect Soil-Profile Distribution of Roots?

No-till (NT) often causes prominent stratification of C and nutrients in the soil profile relative to tilled systems. We hypothesize differences in root distribution within the soil profile between NT and tilled systems could be one factor contributing to stratification. We evaluated how NT affects root length density (RLD), root biomass yield (RBY), and root diameter compared with other tillage systems and factors that may affect root characteristics. We reviewed studies until 23 January 2024 where RLD, RBY, or root diameter were reported under NT and tillage. The data on RLD, RBY, and diameter were tabulated and the weighted log response ratio (MLRR) and confidence intervals computed. Our meta-analysis showed NT increased RLD in the 0-10 cm depth, but reduced RLD at 10-20 cm. It increased RBY and diameter in the 0-20 cm depth and reduced both characteristics at 20-30 cm. Regardless of root characteristic, NT had mixed effects below 30 cm. However, across the soil profile (minimum 50 cm depth), NT had no effect on RLD and RBY. No-till-induced changes in roots can be related to increased compaction at the tillage interface. No-till stratified both RLD and RBY compared with high intensity tillage systems, although there were some conditions where NT stratified only RLD or RBY. No-till did not induce stratification of RLD and RBY in dry regions, mild or hot climates, in medium-textured soils, or compared with intermediate intensity tillage systems. Overall, NT can result in stratification of both RBY and RLD compared with high intensity tillage systems.