Nitrogen effects on species’ contributions to grazed pasture mixtures under nitrogen loss and application restrictions

New regulations to the use of N fertiliser will impact on seed mixture decisions for new pastures. To help inform these decisions, the effects of N on species and species interactions in pasture mixtures were examined. Ten mixtures of perennial ryegrass (PR), white clover (WC) and plantain (P) were sown on 31 March 2017 and grown ±N fertiliser (275 kg/ha in Year 1 reduced to 200 kg N/ha/year) under grazed and irrigated conditions at Lincoln University. After 4 years, an equi-proportional mixture of PR and WC (based on seed count) optimised average total yield (TY), weed yield (WY), metabolisable energy (ME) and crude protein (CP) regardless of N level. The optimal sowing rate was 12.2 kg PR and 7.0 kg WC/ha. Average TY of the optimal mixture was 20.5 t DM/ha/year with 4% WY, 11 MJ/kg DM ME and 21% CP. Pasture yield and quality responded to change in species proportions away from the optimal mixture, including the addition of P. The magnitude of the TY and WY responses was greater with than without N fertiliser because the identity effects of PR and P, and the way all three species interacted, depended on N level.