The effect of red clover (Trifolium pratense L.) variety and chemical nitrogen fertiliser application rate on herbage production and clover content in perennial ryegrass (Lolium perenne L.) red clover silage swards

Red clover ( Trifolium pratense L.; RC) inclusion in perennial ryegrass ( Lolium perenne L.; PRG) silage swards reduces nitrogen (N) fertiliser requirements; however, maintaining production over time remains challenging. Effects of RC variety, N fertiliser rate, and location on herbage production and RC content of PRG-RC silage swards were evaluated over three years. Eight RC varieties were sown with PRG at two Irish sites (Moorepark, Co. Cork and Grange, Co. Meath) with three N rates (0, 75 and 150 kg N/ha/year; 0 N, 75 N, 150 N). Plots were harvested three times annually. In Year 1, herbage production (mean ± SE; 17693 ± 460 kg dry matter (DM)/ha) and RC content (563 ± 27.0 g/kg DM) did not differ among varieties. By Year 3, both declined on average, but Aberclaret and Fearga maintained the highest yields (12524 ± 460.3 kg DM/ha) and the same RC content (563 ± 27.0 g/kg DM). Cut 1 herbage production was greatest with 75 N in Years 1 and 2 and 150 N in Year 3, when RC content had declined. Cut 1 RC content did not differ among N rates, while for Cut 2 and 3, N reduced RC content and had no production benefit except in Year 2 (75 N). Herbage production was 15% greater and RC content 46% lower at Grange vs Moorepark. Results highlight significant variation among RC varieties in production across years and indicate that targeted N fertiliser use can enhance yields when RC content is low. Findings underscore the importance of multi-site, multi-year RC variety evaluations.