Abstract Pastoral agriculture can have negative environmental impacts. These include greenhouse gas emissions (such as enteric CH4 and soil N2O emissions), NH3 volatilisation, and leaching of nitrogen into waterways. We used a modelling approach to assess the effect of three plant traits and one management practice on N2O emissions, nitrogen (N) losses via leaching and NH3 volatilisation, pasture production and soil organic carbon (SOC) changes (as applicable). The aim was to identify traits/management practices that could potentially be environmentally beneficial and could then inform future research to find or breed plants with those traits. The traits and practice investigated were: 1) N content in animal feed; 2) plant-excreted nitrification inhibitors; 3) deep rooting; and 4) frequency of pasture renewal. Of these, the N content in animal feed provided the most promising results, with low N content resulting in lower urine N excretion, and consequently reduced leaching losses and emissions of N2O and NH3. Modelling the effect of plant-excreted nitrification inhibitors showed mixed results, with reduced leaching rates but increased NH3 emissions. N2O emissions could be reduced if nitrification rates were strongly reduced. However, at lower rates of inhibition, there was little effect on N2O emissions. In the deep rooting scenarios, we found that N leaching losses were minimised if roots grew predominantly in upper soil layers where any mineral N was likely to spend more time before being leached. Nitrogen was, therefore, more effectively intercepted and prevented from leaching by greater root proliferation in the upper rather than deeper layers. For pasture renewal, we unexpectedly found that SOC could be increased by more frequent pasture renewal. However, this would come at the cost of reduced pasture production as renewal events reduced grazing off-takes proportionately more than the reduction in carbon gain by pasture plants. A renewal period of about 10 years was found to be optimal for pasture production and could be maintained with minimal SOC changes.

中文翻译：

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减少放牧牧场环境影响的四种不同选择的潜在有效性。基于模型的评估

摘要 牧区农业会对环境产生负面影响。这些包括温室气体排放（例如肠道 CH4 和土壤 N2O 排放）、NH3 挥发和氮渗入水道。我们使用建模方法来评估三种植物性状和一种管理实践对 N2O 排放、通过浸出和 NH3 挥发造成的氮 (N) 损失、牧场生产和土壤有机碳 (SOC) 变化（如适用）的影响。目的是确定可能对环境有益的性状/管理实践，然后可以为未来的研究提供信息，以寻找或培育具有这些性状的植物。研究的性状和实践是：1）动物饲料中的N含量；2) 植物排泄的硝化抑制剂；3）根深蒂固；4) 牧场更新频率。这些，动物饲料中的 N 含量提供了最有希望的结果，低 N 含量导致较低的尿 N 排泄，从而减少了 N2O 和 NH3 的浸出损失和排放。对植物排泄的硝化抑制剂的影响进行建模显示出不同的结果，浸出率降低，但 NH3 排放增加。如果硝化率大幅降低，N2O 排放量就可以减少。然而，在较低的抑制率下，对 N2O 排放的影响很小。在深根情况下，我们发现如果根主要生长在上层土壤中，任何矿物质 N 可能在浸出之前花费更多时间，那么 N 浸出损失会最小化。因此，氮被更有效地拦截并通过在上层而不是更深层的更大的根增殖来防止浸出。对于牧场更新，我们意外地发现可以通过更频繁的牧场更新来增加 SOC。然而，这将以牧场产量减少为代价，因为更新事件减少的放牧量比牧场植物减少的碳增加成比例。发现大约 10 年的更新期最适合牧草生产，并且可以在 SOC 变化最小的情况下维持。