Effect of N fertiliser application rate on herbage production and sward clover content in grazed grass clover plots

Perennial ryegrass-white clover swards can make an important contribution to sustainable ruminant production systems. White clover use in grazed swards in Ireland has been in decline since the 1970s due to the availability and generally low cost of fertiliser nitrogen (N). In recent times there has been renewed interest in white clover use on farms for environmental and economic reasons. The objective of this experiment is to provide information on the interaction between grass-clover swards and N fertiliser in frequently grazed swards. This experiment was a 2x5 factorial arrangement, with two swards (grass only and grass-clover), and five fertiliser N application rates (0, 60, 120, 180, 240 kg N ha(-1)), with three replicates per treatment. Herbage production and sward clover content were measured in 2010 and 2011. Over the two years the grass-clover swards, on average, produced significantly (P < 0.001) more herbage mass (plus 3236 kg DM ha(-1)) than the grass only swards (9944 kg DM ha(-1)). Treatments receiving 0, 60 and 120 kg N ha(-1) produced significantly (P < 0.05) less herbage than treatments receiving 240 kg N ha(-1). As N fertiliser application rate increased, the sward clover content declined.