Undersowing winter oilseed rape with frost-sensitive legume living mulch: Consequences for cash crop nitrogen nutrition

We carried out a field trial over two growing seasons before sowing, comparing seven legume species and three legume mixtures intercropped with rape, and two levels of soil mineral N. The presence of legumes, living during the autumn and dead during the spring, resulted in 20-40 kgN ha−1 more nitrogen uptake in oilseed rape, by the end of flowering, compared to rape grown as a sole crop. Moreover, the use of 15N-labelled nitrogen fertiliser showed that this increase in rape N accumulation was due to the mineralisation of legume residues, but also to other mechanisms such as increase in fertiliser-N recovery and in soil organic matter mineralisation.