Silicon Supply Improves the Rhizodeposition and Transfer of Nitrogen from Trifolium incarnatum L. to Brassica napus L.

The association of legumes with other non-legume plants, such as <i>Brassica napus</i> L., has been reported as an agro-ecological alternative for reducing the nitrogen (N) inputs required for <i>B. napus</i> growth, thanks in particular to the transfer of N compounds from the legume to <i>B. napus</i>. Moreover, recent studies have evidenced that silicon (Si) supply can improve either N uptake by <i>B. napus</i> or the dinitrogen fixation capacity of <i>T. incarnatum</i>. However, the effect of Si supply on the N nutrition of both <i>B. napus</i> and <i>T. incarnatum</i>, especially when growing in association, has not been assessed so far. The aim of this study was to assess the effect of Si supply on the growth of <i>B. napus</i> and <i>T. incarnatum</i> cultivated in association by focusing particularly on N rhizodeposition by <i>T. incarnatum</i> and its transfer to <i>B. napus</i>. The experiment was performed for 10 weeks under a split-root system combined with an ¹⁵N labeling method. The results showed that the Si supply increased the amount of rhizo-deposited N by <i>T. incarnatum</i> by over 40% and enhanced its transfer to <i>B. napus</i>. The transferred N was allocated mainly to pods (17%), as their biomass increased under Si supply. For the first time, this study demonstrates that the association with legume plants together with the Si supply could be an effective approach to improve the agro-ecological balance of <i>B. napus</i>.