A pilot study with 18 dairy farms in recharge areas of five vulnerable drinking water abstractions in the Dutch province of Overijssel aimed to reduce nitrate leaching risks to the upper meter of groundwater through improved farm management. The pilot employed a voluntary, mutual gain approach, promoting measures that enhanced both nutrient efficiency and groundwater quality. Over the research period (2011–2017), nitrogen surpluses on the soil balance declined significantly from 153 to 96 kg N per ha per year, achieving the target of 100 kg N per ha per year. Despite this decline, average nitrate concentrations in the upper meter of groundwater fluctuated annually, showing no significant reduction in grassland but a noticeable decrease in maize. Economic evaluation showed that relative fodder profitability (RFP) increased over time, suggesting positive financial effects of implemented measures, as acknowledged by participating farmers. However, the adoption of measures perceived as complex or less financially rewarding remained limited, highlighting the challenges of relying solely on voluntary implementation. The absence of farm-specific feedback on nitrate leaching emerged as a critical limitation, emphasizing the need for additional monitoring tools, such as residual soil nitrogen assessments, to provide actionable insights at the farm or field level. These findings underscore the potential for further reducing nitrate leaching through enhanced feedback systems, precise execution of measures, and collaborative efforts integrating farmer expertise and scientific knowledge.

This paper presents the Dutch ‘Delta Plan for Agricultural Water Management’ (in Dutch: ‘Deltaplan Agrarisch Waterbeheer’; DAW). This is a voluntary, tailor-made initiative in which farmers, water authorities and their organisations work together to achieve environmental objectives, and to prevent damage caused by droughts and floods, while ensuring an economically strong and sustainable agricultural sector. Drawing on a decade of DAW experiences, this study highlights achievements, lessons learned, and future challenges. Results show that, even though DAW is under pressure due to a shortage of independent advisors, DAW facilitated information and knowledge exchange, and trust-building, which supports participating farmers to improve agricultural management practices. Furthermore, the voluntary nature of DAW, while a strength in that it enables farmers to adopt measures tailored to their specific circumstances, also results in a fragmented pattern of participation. This uneven uptake makes it difficult to assess the effectiveness of measures at the farm scale in relation to the realisation of contributing to EU objectives, such as the European Water Framework Directive (WFD).