Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria 3010, Australia.
J Dairy Sci. 2012 Jul;95(7):4153-75. doi: 10.3168/jds.2011-5110.
The irrigated dairy industry in southern Australia has experienced significant restrictions in irrigation water allocations since 2005, consistent with climate change impact predictions for the region. Simulation models of pasture growth (DairyMod), crop yield (Agricultural Production Systems Simulator, APSIM), and dairy system management and production (UDDER) were used in combination to investigate a range of forage options that may be capable of sustaining dairy business profitability under restricted water-allocation scenarios in northern Victoria, Australia. A total of 23 scenarios were simulated and compared with a base farm system (100% of historical water allocations, grazed perennial ryegrass pasture with supplements; estimated operating surplus $A2,615/ha at a milk price of $A4.14/kg of milk solids). Nine simulations explored the response of the base farm to changes in stocking rate or the implementation of a double cropping rotation on 30% of farm area, or both. Five simulations explored the extreme scenario of dairying without any irrigation water. Two general responses to water restrictions were investigated in a further 9 simulations. Annual ryegrass grazed pasture, complemented by a double cropping rotation (maize grown in summer for silage, followed by either brassica forage crop and annual ryegrass for silage in winter and spring) on 30% of farm area, led to an estimated operating surplus of $A1746/ha at the same stocking rate as the base farm when calving was moved to autumn (instead of late winter, as in the base system). Estimated total irrigation water use was 2.7ML/ha compared with 5.4ML/ha for the base system. Summer-dormant perennial grass plus double cropping (30% of farm area) lifted operating surplus by a further $A100/ha if associated with autumn calving (estimated total irrigation water use 3.1ML/ha). Large shifts in the forage base of dairy farms could sustain profitability in the face of lower, and fluctuating, water allocations. However, changes in other strategic management policies, notably calving date and stocking rate, would be required, and these systems would be more complex to manage. The adaptation scenarios that resulted in the highest estimated operating surplus were those where at least 10 t of pasture or crop DM was grazed directly by cows per hectare per year, resulting in grazed pasture intake of at least 2 t of DM/cow, and at least 60% of all homegrown feed that was consumed was grazed directly.
澳大利亚南部的灌溉奶牛业自 2005 年以来，其灌溉水配给受到了重大限制，这与该地区气候变化影响的预测一致。使用牧场生长模拟模型（DairyMod）、作物产量模拟模型（农业生产系统模拟器，APSIM）和奶牛系统管理和生产模拟模型（UDDER）相结合，研究了一系列可能在澳大利亚维多利亚北部受限制的水配给情景下维持奶牛业盈利能力的饲料选择。总共模拟了 23 种情景，并与一个基础农场系统进行了比较（100%历史配水量，放牧多年生黑麦草牧场，辅以补充饲料；在牛奶价格为 4.14 澳元/公斤牛奶固体的情况下，估计运营盈余为 2615 澳元/公顷）。9 种模拟方案探索了基础农场对畜群密度变化或在 30%农场面积上实施双季轮作的响应，或两者兼而有之。5 种模拟方案探索了在没有任何灌溉水的情况下进行奶牛养殖的极端情况。在另外 9 种模拟方案中，进一步研究了对水限制的两种一般反应。在与基础农场相同的畜群密度下，每年黑麦草牧场放牧，辅以 30%农场面积的双季轮作（夏季种植青贮玉米，然后在冬季和春季种植芸苔属饲料作物和一年生黑麦草作为青贮饲料），预计运营盈余为 1746 澳元/公顷，而基础系统中的产犊时间则推迟到秋季（而不是基础系统中的冬季后期）。估计总灌溉用水量为 2.7ML/ha，而基础系统为 5.4ML/ha。如果与秋季产犊（估计总灌溉用水量为 3.1ML/ha）相结合，夏季休眠多年生牧草加双季轮作（30%的农场面积）可使运营盈余增加 100 澳元/公顷。奶牛场饲料基础的重大转变可以在较低且波动的水配给情况下维持盈利能力。然而，需要改变其他战略管理政策，特别是产犊日期和畜群密度，并且这些系统的管理将更加复杂。导致估计运营盈余最高的适应情景是，每公顷每年至少有 10 吨牧场或作物 DM 被奶牛直接放牧，导致奶牛摄入至少 2 吨 DM/头，并且至少 60%的所有自产饲料都被直接放牧。
