Effects of cover crops on maize establishment, root mycorrhizal colonization, plant growth and grain yield depend on their botanical family: A global meta-analysis

The current literature reports contradictory information regarding the effects of cover crops (CCs) on maize productivity. Quantifying the available information helps drawing robust conclusions that may have important implications for research and policy. Previous meta-analyses investigated the potential effects of CCs on maize biomass and grain yield but with a very narrow focus in terms of geographical areas, explanatory and response variables. A broader geographical coverage would help drawing robust conclusions regarding the effects of CCs on the subsequent maize crop performance. In light of this, we conducted a global meta-analysis to investigate whether management practices and environmental conditions related to CCs (i.e. explanatory variables) affect maize seed germination and seedling emergence, root colonization by arbuscular mycorrhizal fungi, plant height, biomass growth, and grain yield (i.e. response variables) compared to a no CC treatment (i.e. control). Our database included 5 185 comparisons totalling 53 127 observations from 275 publications between 1967 and 2022, worldwide. Overall, CCs reduced maize seed germination and seedling emergence while they enhanced maize root colonization by arbuscular mycorrhizal fungi, biomass and grain yield. When data were analyzed by CC families, three different groups were identified with Fabaceae, Brassicaceae and Poaceae showing the most beneficial, neutral and negative effects, respectively, on most of the response variables. While CC mixtures often enhanced maize performance, higher than three-species mixtures strongly affected maize grain yield. Overall, cover cropping into maize cropping systems, especially under low nitrogen fertilization, maintains or enhances maize productivity while also providing other ecosystem services.