Sustainable management in agriculture is needed to reduce negative side-effects of current intensive land use. The use of cover crops, grown in the seasons without main crops, is one of the options to increase sustainability in agricultural practices by diversification of the cropping system. During growth, cover crops can reduce nutrient losses, while after incorporation of residues they stimulate nutrient cycling in the soil, enhance soil organic matter content and stimulate the microbial community in the soil. Cover crop mixtures rather than monocultures can have even greater positive effects via increased plant complementarity and residue diversity. During decomposition of cover crop residues, we showed that mixtures increase microbial functional diversity and stimulate microbial groups involved in nutrient cycling. This indicates a promising perspective to use cover crop mixtures in the field. However, in our 4-year field experiment, we did not find differences between monocultures and mixtures in nutrient use efficiency (greenhouse gas emissions) or microbial growth or diversity.