Legume‐Based Swards With No or Low Nitrogen Fertiliser Matched or Exceeded Yields of Perennial Ryegrass With Higher Nitrogen Fertiliser

There is an increasing need for low nitrogen (N) grassland systems that minimise greenhouse gas (GHG) emissions while maintaining forage production. Within the context of constrained fertiliser inputs (≤ 100 kg ha −1 year −1 ) for feedstock production systems for grass‐based anaerobic digestion (AD), we investigated the effects of grassland species diversity, N source, and N application rates on both forage and nitrogen yield. In a two‐year field experiment, plots received either digestate from an AD plant or calcium ammonium nitrate (CAN) at rates ranging from 0 to 100 kg N ha −1 year −1 . Higher‐diversity swards (grass‐legume communities and a six‐species mixture of grasses, legumes, and herbs) with lower N (0 or 50 kg ha −1 year −1 ) consistently matched or outyielded L. perenne with 100 kg N for both dry matter and N yield. Averaged across the 2 years, both the perennial ryegrass + red clover community and the six‐species mixture with zero N fertiliser achieved a higher (more usually) or similar yield and nitrogen yield to that of the L. perenne monoculture with 100 kg ha −1 year −1 N fertiliser. Legumes achieved high N yield in monocultures, and T. pratense outperformed a wide range of mixture compositions. There were community‐specific effects of both N source and rate on yield, but no effects of N source and rate on N yield. These results suggest that legume‐containing multispecies grassland mixtures can deliver high forage yield within low‐nitrogen grassland systems, and support productive grassland systems under increasingly stringent fertiliser and environmental regulations.