Comparison of grassland management systems for beef cattle using self-contained farmlets: effects of contrasting nitrogen inputs and management strategies on nitrogen budgets, and herbage and animal production

Past research on nitrogen (N) inputs, losses and surpluses focused on separate components of grassland management, i.e., grazed or cut swards and the impact of fertiliser or slurry applications. In practice, however, grassland is both grazed and cut for conservation, and N fertiliser is supplied from both organic and inorganic sources. A whole systems approach was used to evaluate the effects of combinations of management strategies designed to reduce N losses on N budgets, and herbage and animal production in South West England. Three systems with contrasting N inputs were compared: CN, conventional mineral N application and broadcast slurry; TN, tactical mineral N application with slurry injection and the early housing of cattle; GC, a mixed grass/white clover sward with no mineral N addition and slurry injection. Comparisons were made on two contrasting soil types: a freely-draining sandy loam (Gleysol, Site 1), and a poorly drained clay (Luvisol, Site 2). 1 ha farmlets were grazed to a target sward height by beef cattle for a 5-year (Site 1) or a 4-year (Site 2) period. Herbage surplus to grazing requirements was cut for silage. On average, 185 kg N ha⁻¹ was applied annually to treatment TN compared with 280 kg N ha⁻¹ for CN. An additional 76, 102 and 67 kg N ha⁻¹ was applied in slurry to treatments CN, TN and GC, respectively. Substantial reductions in N surpluses were achieved for both treatments TN and GC compared with treatment CN (N surpluses ha⁻¹: 254, 168 and 119 kg at Site 1, and 247 kg, 190 and 73 kg at Site 2, for CN, TN and GC, respectively). The highest N input for treatment CN was associated with the greatest animal and herbage production. More land was required for grazing on treatment GC and less herbage was cut for silage so that self-sufficiency was not attained for winter fodder on this treatment. The early removal of cattle on treatment TN did not result in a significant increase in the amount of herbage cut for silage. It was concluded that the combinations of mitigation options used were successful in reducing N surpluses compared with the conventional N management system, but animal and herbage production was reduced.