Objective  Since long-term conventional agriculture emphasizes utilization and production rather than protection, and continuous planting of maize has led to the imbalance of soil nutrients and the decline of soil health, the impact of intercropping with cover crops and maize has been carried on soil carbon and nitrogen contents and related enzyme activities, which will provide scientific evidence for the promotion of conservation tillage patterns in Northeast China.

  Method  This study investigated impacts of three cover crops (Medicago sativa L., Vicia villosa R. and Lolium multiflorum L.) on soil nutrients and enzyme activities under the intercropping of cover crops and maize.

  Result  Our results showed that different planting patterns and cover crops affected significantly soil nitrogen content and enzyme activities in the cover crop-maize intercropping systems, only different planting patterns impacted on soil carbon content. At maize jointing stage, intercropping maize and alfalfa treatment increased significantly mineral nitrogen, so nitrate nitrogen and ammonium nitrogen content increased 14.94 mg kg⁻¹ and 2.07 mg kg⁻¹, and L-leucine aminopeptidase activities increased 17.9 nmol g⁻¹ h⁻¹. Compared to other crops, hairy vetch increased significantly activities of β-N-acetylglucosaminidase and L-leucine aminopeptidase. In the intercropping hairy vetch system, the activities of peroxidase and polyphenol oxidase were significantly increased 12.65% and 66.94% than those in the intercropping ryegrass system. At the maize mature stage, contents of soil organic carbon and total nitrogen in maize monoculture and intercropping were increased significantly compared with those in cover crop monoculture, but no significant effects on enzyme activities. The results of redundancy analysis showed that ammonium nitrogen content was likely important environmental factor of soil enzyme activities among treatments.

  Conclusion  Intercropping maize and legumes increase contents of soil available nitrogen and activities of soil enzyme, also enhance the potential and availability of nitrogen conversion. Therefore, alfalfa and hairy vetch are optimum cover crops in this region.