Can lysimeters be used to reduce emission in soil based glasshouse horticulture?

The ecological surface water quality in areas with intensive glasshouse horticulture in the Netherlands is not fulfilling the goals of the EU Nitrates Directive and Water Framework Directive. Opposite to soilless grown crops with obligatory recycling of drainage water, emission in soil based growing systems is difficult to manage. For some crops the conversion from soil based to soilless systems is economically (e.g., chrysanthemums) or principally (organic horticulture) not an option. In the Netherlands a steady approximately 20% of the total glasshouse horticulture is therefore soil based. Since greenhouse production occurs yearround and at a high level, the amounts of water and nutrients used are much higher than in field crops. Thus emission of excess water and nutrients to the ground water and open surface water is likely to occur. The Dutch policy is aiming to tackle the problem of emission at its source. Therefore, we need methods to apply water and nutrients at rates equal to the crop demand. We recently started a project to develop a decision support system for the growers for achieving this goal and thus to minimize the leaching to the ground water and discharge to open surface water. The system exists of a lysimeter in the glasshouse to collect excess water and nutrients, water content sensors inside and outside the lysimeter, and models to determine, guide and predict evapotranspiration and leaching. At eight commercial farms the system has been implemented. Via local discussion groups neighboring growers can discuss the findings obtained at the test locations. These discussions are then used to further develop the decision support system and to develop best practices for the growers. We will present our approach and give some first illustrative results.