Consumers expect that the production of organic vegetables is less harmful to the environment compared to conventional vegetable cropping. However, vegetables with a high nitrogen demand such as cauliflower may cause intensive leaching of nitrate to natural waters in conventional as well as in organic production. In addition, organic growers face difficulties in providing adequate amounts of organic fertiliser in order to attain high yields due to the scarcity of organic livestock manure. In organic cropping systems, the use of an in-season living mulch may decrease the need for fertiliser and the risk of nitrate leaching. It may also improve nitrogen nutrition for next season’s crop. The aim of this study was to investigate the effect of growing an in-season living mulch of grass-clover on cauliflower yields, nitrate leaching over winter, and soil nitrogen availability the following spring. A field experiment was performed on a sandy loam soil using two varieties of cauliflower and with or without grass-clover as living mulch. The mulch consisted of an overwintering grass-clover that was incorporated in strips before the planting of cauliflower, and two levels of fertilisation (dried chicken manure) were applied. Plant samples were taken for evaluation of marketable and non-marketable yields, and for analysis of dry matter and nitrogen content. Evaluation of inorganic N-content in the soil was done at planting, at harvest, in late autumn and in spring by taking soil samples to a depth of 1.5 m. Results show that high yields of cauliflower can be maintained per meter plant row, whereas no effects on nitrate leaching could be observed in a cropping system with an in-season living mulch of grass-clover
