Optimisation of N fertilisation in Italian ryegrass (Lolium multiflorum L.) seed production

For most crops, N fertiliser advice is available and increasingly used among farmers in Belgium. The N fertilisation of Italian ryegrass (Lolium multiflorum L.) for seed production is based on farmer’s experience as little field trial information is available to define a fertiliser recommendation. Eight field trials (2008 - 2015) were conducted in sandy loam soil to determine optimal N fertilisation. Logistic modelling revealed that maximum seed yield can be obtained when 141 kg N ha-1 is available (N mineralisation + fertilisation). This corresponds to an average fertilisation of 92 kg N ha-1 after the forage cut, either in a single application or as a split application. In a split application, 60 kg N ha-1 should be fertilised after the forage cut and additional N should be supplied when the NNI (nitrogen nutrition index) at the two to three node stage (BBCH 32 - 33) is below the critical point (0.83).