No‐Till Legume Cover Crops Enhance Soil Carbon, Mitigate Greenhouse Gas Emissions, and Increase Yield in Dryland Wheat: A Global Meta‐Analysis

Global drylands, essential for wheat production, are increasingly threatened by climate change and conventional agricultural practices that degrade soil and intensify greenhouse gas emissions. This study presents the first global meta‐analysis quantifying the individual and combined effects of no‐till (NT), legume cover crops (LCC), and nonlegume cover crops (NLCC) in dryland winter wheat systems, with an explicit comparison of short‐term (< 10 years) and long‐term (≥ 10 years) adoption. The analysis synthesizes 4927 field observations from 132 studies across five conservation systems, benchmarked against conventional tillage (CT) with bare fallow. The NT‐LCC system significantly enhanced soil organic carbon (SOC) by 28.5% ( p < 0.001), microbial biomass carbon (MBC) by 23.1% ( p < 0.001), water‐use efficiency (WUE) by 29.4% ( p < 0.01), nitrogen‐use efficiency (NUE) by 27.2% ( p < 0.05), and grain yield by 24.1% ( p < 0.05), while reducing nitrous oxide (N 2 O) emissions by 16.2% ( p < 0.01) and methane (CH 4 ) emissions by 13.5% ( p < 0.05). In contrast, NT alone increased SOC by only 8.7% and reduced N 2 O by 6%, while CT + LCC increased SOC by 12.3% ( p < 0.05). These benefits were strongly time‐dependent: under NT‐LCC, long‐term adoption increased SOC by 45.2% (compared to 28.5% for short‐term; p < 0.001) and reduced N 2 O by 24% (compared to 16% for short‐term; p < 0.01), with correspondingly greater improvements in WUE, NUE, and grain yield ( p < 0.05). Environmental factors hierarchically controlled efficacy, with optimal results observed in fine‐textured soils receiving more than 600 mm annual precipitation. Structural equation modeling identified SOC as a key factor associated with improved resource efficiency and reduced emissions, while other edaphic and management factors also contributed significantly. Overall, NT‐LCC enables sustainable intensification and directly contributes to land degradation mitigation and soil restoration in vulnerable dryland agroecosystems, with its full potential realized through long‐term commitment in suitable agro‐ecological contexts.