N-TOOLBOX Case Studies: a summary of experiences

In each of the four partner countries we tested the N-Toolbox approach on farms. This involved:

  1. identifying a target region/area where nitrate pollution was a known risk
  2. engaging with farmers in the area and identifying individuals who were interested in working with scientists to test and evaluate some N loss reducing strategies on their farms
  3. selecting some strategies expected to reduce N losses and/or improve N use efficiency on the case study farms
  4. monitoring N dynamics on the case study farms and simulating dynamics using NDICEA
  5. interpreting results of the case studies and reporting back to participating farmers
  6. evaluation of the engagement of farmers and the role of NDICEA

Read on to find out how these steps were implemented in each country.


A Stakeholder Advisory Group (SAG) in Spain advised the scientists on the best target areas for on-farm case studies.  Two maize producing, irrigated areas in Central Spain were selected.   The goal was to optimize both nitrogen and water management to reduce nitrate leaching.  The key message used to engage farmers was that it is possible to maximize profit by reducing fertilizer rates if water and fertilizer management are adapted to crop needs.

Advisors had an important role in knowledge transfer and tools like NDICEA reinforced the technical value of their message

The SAG also provided the following valuable advice:

  1. advisors have a large influence on the decisions taken by farmers, therefore, it is essential to work with advisors to engage farmers
  2. identify a short list of relevant strategies to prevent nitrate losses in irrigated systems and discuss it with farmers, rather than present the detailed catalogue of strategies in full to the farmers

Nitrogen balance studies and local experiments were used to demonstrate to farmers that N applications were often excessive.  Beyond the optimal rate there was often no crop response to N fertilizer. The farmers were already familiar with the problem of excess fertilizer application, but they really appreciated that the problem was approached as a strategy to reduce costs.

The role of NDICEA in farmer engagement was to serve as a starting point for discussion, and also to provide a handy tool for comparing the effect of the potential strategies on the different components of the N cycle

NDICEA answers the question: where has my N fertilizer gone?

Farmers really wanted to know: where is the fertilizer going? NDICEA was very useful to answer this question.  Farmers were very interested in learning about the N balance on their own farm. They had already heard about nitrate leaching, volatilization and denitrification, but looking at figures of their own agricultural systems was very useful to design specific strategies for their farm.

 Farmers selected in the project tended to be those who are already progressive and engaged; it is difficult to know whether lessons learned from this group will be transferable to the wider farming community.

Farmers were not willing to learn how to use NDICEA, but were interested in participating in discussions about its outputs. Advisors were interested in learning how to use NDICEA, and they found it a useful tool to conduct N balances in agricultural systems and to support recommendations to farmers

United Kingdom

  • work with existing networks of farmers and other stakeholders
  • don’t inundate farmers with requests to participate in projects

N-Toolbox case study activities in England were focussed on optimising fertilizer recommendations. This was identified as a strategy that would require minimal investment by the farmer and could result in an economic benefit.
The Eden Valley region of northwest England was chosen as a focus area for N-Toolbox case study activities.

<insert picture Eden Valley in England>

Through a number of networks (government contacts, a private charity working on Eden River water quality, a local farmers network, word of mouth) interested farmers for the case studies were identified.

The farmers quickly grasped the purpose of the NDICEA software tool and were engaged and interested when it was demonstrated. The use of the tool provided a useful stimulus for discussion about soil N dynamics in their fields and what factors could be controlling these dynamics. Cases where the tool did not accurately predict actual N dynamics i.e. where soil mineral N measurements did not match the model predictions, proved to be particularly useful for stimulating discussions and debate. So the accuracy of the model did not prove to be particularly important when using it as a demonstration tool in the context of the farmer meetings.

The use of the case studies served to dispel some of the assumptions about fertilizer use on farms and N losses. None of the farmers believed that they were over-using nitrogen inputs (due to cost and need for efficient uptake) and this was proved so in the trials. In fact, two of the three host farms in the 2010-2011 trials were under-using N inputs according to the results.

<insert picture field trial in Eden Valley 2011>

The Netherlands

The combination of horticultural production and sandy soils in The Netherlands makes management of nitrogen particularly challenging.   Researchers worked closely with advisors to identify farmers interested in trying out strategies to reduce their N losses.  Several measures of the N-toolbox were discussed and successfully experimented with by the researchers and farmers. Nevertheless, some agronomic and economic limitations to the application of N-toolbox measures became apparent during the N-toolbox project.

One of the measures which proved useful was the NDICEA nitrogen dynamics model. NDICEA simulations showed that most of the nitrogen loss occurs during winter. This can possibly be reduced by changes in the fertilizer management aiming at a better match between crop demand and nitrogen availability, and by sowing catch crops in autumn after the main crop.


Available Nitrogen

Nitrogen Leaching

Slow release nitrogen fertilizers can be of help synchronising the N-dynamics of soil and plant. 

The interaction with farmers and the trials in the field revealed some important drawbacks to the use of catch crops and green manures. First, the timing of planting is crucial: sowing a green manure after September 20th in The Netherlands seems to be useless because growing conditions for most crops are too poor.

Also, farmers are well aware that many green manure species enhance nematodes. Knowledge about which nematode is enhanced by what green manure is widespread and taken into account by selecting the green manure, but, as a farmer summarized: “The perfect green manure does not exist.” Costs, fear of nematodes and timing issues seem to be the most important limitations for widespread adoption of green manures in arable farming throughout The Netherlands.

  • slow release fertilizers were not appropriate in the sandy soil
  • catch crop establishment can be poor if planted too late
  • farmers are concerned about nematode risks when growing green manures

NDICEA as a decision support tool was mainly used by the researchers who are already familiar with the model. They used it first, to better understand the system at stake and to evaluate proposed methods with the farmers, and second, to show farmers the effects of different amounts or types of fertilizer used. For the farmers the model and the presentation of the nitrogen dynamics were completely new. Although they were all very interested, acceptance of the results by farmers is not always assured.


  • winter green manures and spring manure applications can increase N leaching risk - even on organic farms
  • NDICEA can illustrate for farmers the excess N levels in their soil
  • fertilizer rates can be reduced
  • conventional farmers were introduced to autumn catch crops

Intensive vegetable crop rotations on both organic and conventional farms were targeted because of prior knowledge about the high fertilizer rates and low nitrogen use efficiency in these systems.  Some organic farms were chosen because many were using high rates of manure after incorporation of winter green manures in spring and it was leading to a high risk of leaching.  The Ntoolbox strategy of reduced fertilizers was implemented and directed to both organic and conventional farmers.  By measuring soil mineral N to 1.5-2 m depth and NDICEA modelling of the availability of soil nitrogen in the crop root zone, farmers were shown the nitrogen availability to the crop over the season, and the possibility to save on spring applications of fertilizer. 

The fact that farmers were promised information about soil nitrogen over time in the root zone of their fields was clearly a factor that stimulated the farmers’ interest in the project

<insert picture deep soil sampling in Denmark>

The joint activities from both the Ntoolbox project and the advisory service on implementing strategies to reduce nitrogen leaching were clearly important for the engagement of the organic farmers.

Researchers visited the farms and discussed the idea of reducing fertilizer rates for the benefit of the environment and farmer’s profits. The farmers valued the opportunity to get in depth knowledge about nitrogen dynamics in their fields. NDICEA was demonstrated to the farmers by the advisor, who was keen on using the model in his daily advisory activities, and who wanted to test the model for decision support.

These differences were discussed among the participants and were clearly eye-openers with comments from farmers like “well, then we could have skipped the spring fertilizer application”

The farmers showed good interest in the demonstration of the NDICEA model, but did not seem interested in using it on their own, but in collaboration with the advisory service. This was despite the fact that the farmers participating in the Ntoolbox project were exceptionally engaged and knowledgeable about the environmental and biogeochemical aspects of reducing nitrogen losses from their systems.

The Danish national advisory service is now working to implement NDICEA as an advisory tool on Danish farms.

Meetings were held among farmers, the advisor and a representative from the national environmental authorities to discuss project results. In some cases the results clearly showed the high spring soil nitrogen availability from green manures and last year’s residual soil N at one organic and one conventional farm. This demonstrated to farmers that the spring fertilizer additions were more or less unneeded and could lead to excess nitrogen availability during the growing season and high nitrogen leaching losses during winter.

Key lessons from the case studies

    • The expectation of knowledge transfer on nitrogen cycling and production information specific to each farmer’s own farm was a main driver for the engagement of farmers in the Ntoolbox project.
    • The prospect of economic benefit from implementation of strategies was a key factor for engaging farmers.
    • The nitrogen simulation model NDICEA was an important tool for knowledge transfer and stimulation of discussions on nitrate leaching with farmers.