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

The use of legume cover crops as green manure is often seen as an effective means of supplying nitrogen to the following crop. As winter oilseed rape requires a large amount of N in the spring, the introduction of frost-sensitive legume living mulch (killed off during the winter) is a promising way of decreasing mineral N fertiliser inputs. The aim of this study was to assess the supply of biological N to rape during the spring from several frost-sensitive legumes, grown as intercropped living mulches. 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 N-15-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. (C) 2016 Elsevier B.V. All rights reserved.