标题：A Comparison of Grassland Management Systems for Beef Cattle Using Self-Contained Farmlets: Effects of Contrasting Nitrogen Inputs and Management Strategies on the Farm Economy
摘要：The financial implications of manipulating nitrogen (N) inputs and management strategies for beef production systems were assessed. One-hectare grassland farmlets were grazed to a target sward height by beef steers; herbage surplus to grazing requirements was cut for silage. Three systems were compared: ‘CN’, conventional mineral N application to a grass monoculture and broadcast slurry; ‘TN’, tactical mineral N application at fortnightly intervals to a grass monoculture 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 (site 1) and a poorly drained clay (site 2). Financial budgets for 1999-2000 show that estimated gross profit margins (gross outputs minus variable costs), after deducting contractor’s charges for sward preparation and fertiliser spreading, were highest for treatment CN at both sites Î(€1552, €1356 and €1461 ha-1 for site 1 and €1562, €1281 and €1287 ha-1 for site 2, for treatments CN, TN and GC, respectively). Treatment TN was penalised by increased costs associated with an extended housed period and the need to purchase additional silage for winter feeding which cost €242 ha-1 at site 1 and €250 ha-1 at site 2. Savings in N fertiliser for TN in comparison with CN (€44 ha-1 at site 1 and €39 ha-1 at site 2) were more than offset by the increased costs of fortnightly fertiliser applications (€54 ha-1 at site 1 and €46 ha-1 at site 2). Treatment GC benefited from zero costs for the purchase and spreading of mineral N fertiliser but was penalised by increased variation in forage DM production which resulted in a shortfall in winter fodder requirements with a replacement cost of €250 at site 1 and €435 at site 2. The best overall economic performance after the allocation of all possible relevant costs (variable, fixed and capital) in terms of the relative net profit margin, was for GC at site 1 and for CN at site 2 (-€1358, -€2399 and -€1304 ha-1 at site 1 and -€1122, -€2810 and - €1380 ha-1 at site 2, for CN, TN and GC, respectively). The opportunity costs of reducing N surpluses at the gross profit margin level (after contractor’s charges) for treatments TN and GC over treatment CN were calculated at €2.29 kg-1 N surplus for TN and €0.67 kg-1 N surplus for GC at site 1, with corresponding values of €4.91 and €1.57 at site 2.
