DairyNZ Ltd., Private Bag 3221, Hamilton 3240, New Zealand.
DairyNZ Ltd., Private Bag 3221, Hamilton 3240, New Zealand.
Sci Total Environ. 2017 Dec 1;599-600:1791-1801. doi: 10.1016/j.scitotenv.2017.05.104. Epub 2017 May 20.
An efficient dairy system, that implemented a combination of nitrogen (N) leaching mitigation strategies including lower N fertilizer input, standing cows off pasture for part of the day in autumn and winter (stand-off), and importing limited amounts of low protein supplements was evaluated over four consecutive years of a farmlet study. This efficient system consistently demonstrated a lower measured annual N leaching of 40 to 50% compared with a baseline system representing current practice with no mitigations. To maximize return from this system fewer cows but of higher genetic merit were used resulting in an average decrease in milk production of 2% and operating profit by 5% compared with the baseline system. The magnitude of the N leaching reduction from mitigation strategies was predicted in pre-trial modelling. Using similar mechanistic models in a post-trial study, we were able to satisfactorily predict the trends in the observed N leaching data over the four years. This enabled us to use the calibrated models to explore the contributions of the different mitigation strategies to the overall leaching reduction in the efficient system. In one of the years half of the leaching reduction was achieved by the 'input' component of the strategy (less feed N flowing through the herd from lower fertilizer use, less grass grown, and low-protein supplement use), while the other half was achieved by the stand-off strategy. However, these contributions are determined by the weather of a particular year. We estimate that on average stand-off would contribute 60% and 'input' 40% to the reduction. The implication is that farmers facing nutrient loss limitations have some current and some future technologies available to them for meeting these limitations. A shift towards the mitigations described here can result in a downward trend in their own N-loss metrics. The challenge will be to negate any reductions in production and profit, and remain competitive.
一个高效的奶牛养殖系统，采用了氮（N）淋溶缓解策略的组合，包括减少氮肥投入、在秋季和冬季将奶牛从牧场上移开一段时间（停牧），以及限量进口低蛋白补充饲料，在一个农场研究的连续四年中进行了评估。与没有缓解措施的现行做法的基准系统相比，该高效系统始终显示出较低的年测量 N 淋溶量，为 40%至 50%。为了从该系统中获得最大收益，使用了较少但遗传优良的奶牛，导致与基准系统相比，牛奶产量平均减少 2%，运营利润减少 5%。在试验前建模中预测了缓解策略的 N 淋溶减少量。在试验后研究中使用类似的机制模型，我们能够令人满意地预测四年内观察到的 N 淋溶数据的趋势。这使我们能够使用校准模型来探索不同缓解策略对高效系统整体淋溶减少的贡献。在其中一年中，一半的淋溶减少是通过策略的“投入”部分实现的（从较低的肥料使用量、较少的草生长量和低蛋白补充饲料使用量中减少通过牛群流动的饲料 N），而另一半是通过停牧策略实现的。然而，这些贡献取决于特定年份的天气情况。我们估计，平均而言，停牧将贡献 60%，“投入”贡献 40%。这意味着面临养分损失限制的农民有一些当前和未来的技术可供他们使用来满足这些限制。向这里描述的缓解措施转变可能会导致他们自己的 N 损失指标呈下降趋势。挑战将是抵消任何产量和利润的减少，并保持竞争力。
