Root development as a driver of mineral-associated organic matter formation in cover crop systems of high-latitude agriculture

Cover crops enhance soil quality and organic matter stability, yet the mechanisms linking belowground inputs to persistent soil organic matter (SOM) remain unclear. This study examined the effects of diversified cover cropping in barley systems on root biomass, SOM fractions, soil structure, microbial activity, and yield in central Norway (63.9° N), three years post-implementation. Six treatments were tested: (1) Control (barley without NPK), (2) Biochar-Fertilizer (barley + NPK + 3 Mg ha⁻¹ biochar), (3) Monocrop (barley), (4) Ryegrass (barley + ryegrass), (5) Clover (barley + ryegrass + white/red clover), and (6) Chicory (barley + ryegrass + red clover + chicory + bird’s-foot trefoil). Ryegrass and Clover systems produced 28.65 g m - ² more root biomass at 0–13 cm (p < 0.05) and, along with Monocrop, stored 2.2 Mg ha - ¹ more mineral-associated organic matter (MAOM) carbon and 0.2 Mg ha - ¹ more MAOM nitrogen at 0–20 cm than other treatments. The Chicory system improved soil structure and biology, with higher aggregate stability, lower bulk density, and greater microbial abundance. Barley yields remained consistent across treatments, suggesting that cover cropping and low biochar inputs do not reduce productivity. Strong correlations (p < 0.01) between root biomass and MAOM stocks highlight root development as a key driver of SOM stabilization via organo-mineral associations. These findings underscore the role of root-enhancing cover crops in promoting MAOM formation and long-term SOM persistence, offering valuable insights for sustainable soil management. • Mixes of barley, ryegrass, and clovers resulted in higher MAOM and root biomass. • Root biomass significantly correlated with MAOM stocks. • Higher root biomass and N stocks improved barley yields. • Microorganisms abundance and aggregation did not affect SOM Stocks. • We recommend prioritizing root development in high-latitude agriculture.