Production interactions between combinations of 4 perennial legumes and 5 perennial grasses, grown under high input management with and without applications of nitrogen

The value of legumes in high input pastures has come into question in recent years. High sowing rates of grasses (> 20 kg/ha) and the regular use of nitrogen fertilisers are contributing factors to the declining composition of legumes in pastures. However, legumes can be an important component of a mixed pasture sward, through their ability to fix atmospheric nitrogen and their high nutritive value. This study evaluated the dry matter (DM) contribution of legumes to irrigated mixed swards receiving either a nil nitrogen or a 40kg N/ha nitrogen treatment following each defoliation event. The experiment was sown with 29 pasture treatments consisting of mixed swards and monocultures of 5 grass species (perennial ryegrass cv. Base, tall fescue Festuca arundinacea cv. Quantum II MaxP, coloured brome Bromus coloratus cv. Exceltas, cocksfoot Dactylis glomerata cv. Megatas and phalaris Phalaris hybrid cv. Advanced AT) and 4 legume species (white clover cv. Bounty, red clover Trifolium pratense cv. Rubitas, strawberry clover Trifolium fragiferum cv. Palestine and Caucasian clover Trifolium ambiguum cv. Kuratas). The clover contribution (%) to production increased significantly (P<0.05) in nil-nitrogen treatments compared with pasture mixes receiving nitrogen. The application of high rates of N fertilisers can inhibit significant contributions of legumes to overall production. White clover proved to be well adapted and the results of this study suggest it would difficult to justify the sole use of any alternative species tested.