Biogas production on dairy farms is promoted as a climate change measure since it captures methane, a greenhouse gas emitted by manure, and produces renewable energy. Digestate is a by‐product of biogas production and is often used for nutrient recycling in a similar way as traditional manure. Despite having similar functions, manure and digestate have different behaviors related to nitrogen recycling and nitrogen emissions which are significant agricultural and environmental concerns of manure. This paper provides an insight into the impact of biogas production on nitrogen emissions and nitrogen recycling issues of the current dairy farming practice. Using the Substance Flow Analysis (SFA) approach, we analyzed the changes on three levels: manure handling, dairy farm, and the whole chain. Four biogas production options on a Dutch dairy farm related to types and sources of feedstocks were considered. We quantified biogas output, nitrogen fertilizer replacement percentage (%) and consequential nitrogen emissions (kgN/year; kgN/m³ biogas produced) of these productions in comparison with the baseline of current dairy farming without biogas. We conclude that biogas production options with additional feedstocks will cause profound changes in the nitrogen recycling on dairy farms and the nitrogen emissions at the chain level. Besides, the results show that determining the optimal biogas production option can be challenging as the evaluation is highly dependent on the used nitrogen indicator and the included level of analysis. Our findings show how SFA and a multilevel perspective can give a broader understanding of environmental trade‐offs.

中文翻译：

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沼气生产对荷兰奶业系统中氮流量的影响：沼气生产链中氮指标的多级评估

奶牛场的沼气生产可以作为一种气候变化措施而得到推广，因为它可以捕获甲烷，粪便排放的温室气体并产生可再生能源。Digestate是沼气生产的副产品，通常以与传统肥料类似的方式用于营养循环利用。尽管具有相似的功能，但肥料和消化物具有与氮循环和氮排放有关的不同行为，而氮的循环和氮排放是肥料在农业和环境方面的重要问题。本文提供了关于沼气生产对当前奶牛养殖实践中氮排放和氮再循环问题的影响的见解。使用物质流分析（SFA）方法，我们在三个层面上分析了变化：粪便处理，奶牛场和整个链条。考虑了荷兰奶牛场与原料类型和来源有关的四种沼气生产方案。我们量化了沼气产量，氮肥替代率（％）和相应的氮排放量（kgN /年； kgN / m与当前没有沼气的奶牛场的基准相比，这些生产产生了^3种沼气。我们得出的结论是，沼气生产选项和其他原料将对奶牛场的氮循环利用和连锁水平的氮排放产生深刻的影响。此外，结果表明，确定最佳的沼气生产方案可能具有挑战性，因为评估高度依赖于所用的氮指标和所包含的分析水平。我们的发现表明，SFA和多层次的视角如何使人们对环境折衷有更广泛的了解。