One of the main challenges for modern agriculture is closing nutrient cycles better since nutrient deficits as well as nutrient surpluses can cause severe ecological issues. Current efforts to improve nutrient management are mainly focused on the farm level. However, closing nutrient cycles is not only a farm management issue, but also a policy issue. Here the farm should be considered in interaction with other scale levels: regional, national, and international. To develop effective policy interventions a thorough understanding of this complex system and the effects of the policy interventions is needed. The Nutrient Cycle Assessment Tool (NCAT) was developed as a tool to perform ex ante evaluations of policy interventions aimed at closing nutrient cycles in agriculture. To contribute to meaningful change, active involvement of stakeholders in applying the NCAT is essential. This article describes the design of the NCAT, and explains why and how complexity and joint learning, single and double loop learning, and systems thinking approaches are used as the key elements of the design. The NCAT focuses on facts and stimulates participants to postpone value judgements. A case study indicated that the tool provided stakeholders with clear insights in the potential effects of policy interventions. Applying the NCAT can lead to shared and enhanced understanding of the effects and consequences of an intervention among participating stakeholders, which is an important prerequisite when developing implementable and supported policy decisions. Observations and evaluation interviews indicate that this process stimulates cognitive learning as well as relational learning. By reflecting on the case study and the resulting insights, the scientific status of the results from using the NCAT is discussed, as well as its value for policy processes.

现代农业的主要挑战之一是更好地关闭养分循环，因为养分短缺和养分过剩会造成严重的生态问题。当前改善养分管理的努力主要集中在农场一级。但是，关闭养分循环不仅是农场管理的问题，还是政策的问题。在这里，应该考虑将农场与其他规模级别（区域，国家和国际）进行交互。为了制定有效的政策干预措施，需要对这个复杂的系统以及政策干预措施的效果有透彻的了解。营养循环评估工具（NCAT）的开发是为了对旨在结束农业中营养循环的政策干预措施进行事前评估。为了做出有意义的改变，利益相关者积极参与应用NCAT是至关重要的。本文介绍了NCAT的设计，并说明了为什么以及如何以及如何将复杂性和联合学习，单循环和双循环学习以及系统思维方法用作设计的关键要素。NCAT关注事实，并鼓励参与者推迟价值判断。案例研究表明，该工具为利益相关者提供了对政策干预的潜在影响的清晰见解。应用NCAT可以导致参与的利益相关者之间对干预效果和后果的共享和增强理解，这是制定可行且可支持的政策决策时的重要前提。观察和评估访谈表明，这一过程既刺激了认知学习又促进了关系学习。通过反思案例研究和由此产生的见解，讨论了使用NCAT得出的结果的科学状态及其对政策流程的价值。