A cropping system was designed to fulfill the increasing demand for biomass for food and energy without decreasing long term soil fertility. A field experiment was carried out including alternating strips of annual maize (Zea mays L.) and perennial ryegrass (Lolium perenne L.) – clover (Trifolium repens+Trifolium pretense L.) mixture grown in the same field. In autumn an annual strip was established with green-rye (Secale cereale L.) after soil incorporation of a 1st year grass-clover a 6-m wide strip followed by maize sowing in May. The perennial strips were established without incorporating the same 1st year grass-clover in an equivalent 6-m wide strip, resulting in an early competitive advantage for the perennial strip toward the annual strip. Throughout the growing season maize was never able to recovery from this and yields were reduced with around 50% when grown adjacent to grass-clover (0–50cm) compared to with >50cm distance. There was significantly greater clover content in the sward when grown with >150cm distance to maize (30%) compared to the 0–25cm distance (10%) indicating more available soil mineral N in the interface between the strips related to a strong ability of the grass to compete for soil mineral N. Maize yields were clearly associated with N fertilizer application. When fertilizer N was applied through slurry or anaerobic digested slurry maize yields was increasing with up to 100% equivalent to 1200g carbon (C) m−2 or 35MJm−2. However, the same relative growth reduction was found when grown in close proximity to the grass-clover strip. If slurry is available maize secures an efficient N uptake, however, long-term effects of maize cropping and biomass removal on soil quality is of concern. The present strip cropping system did not possess the right balance of co-existence and complementarity with relative yield advantages for the whole crop cycle between 0.96 and 1.01. Thus, the total land area required under traditional cropping attaining the yields achieved when dividing the field in strips is the same. Greater complementarity between strips is needed to gain the potential strip cropping advantages.