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Growers and Dutch government have concluded a covenant in which they express the ambition to reduce the carbon footprint of greenhouse production in order to improve the energy neutrality of newly built greenhouses. Conditioned cultivation in (semi-)closed greenhouses is seen as one of the instruments to reach this goal. It is appointed in the covenant to arrive in 2011 at 700 ha and in 2020 at 2,500 ha semi-closed greenhouses. This paper describes the instruments used to monitor the results of conditioned cultivation in eight semi-closed greenhouses in practice. It addresses the monitoring process, the installations involved and highlights some of the measured data.

Minimisation of nutrient and water loss to the environment, prediction and planning of production and product quality, such that they meet the demands of customers, and increased financial return are some of the goals of current greenhouse horticulture. This requires an integrated system for monitoring and control of the nutrient solution, plant growth and product quality. This paper describes the components of such a system.Tomato was selected as example crop. Plant sensors for photosynthesis, radiation interception and fresh growth rate were developed and tested, and the combined plant-substrate model was validated against greenhouse experiments and commercial growth data. Techniques for auto-calibration of the crop model with sensor information were developed. Scenarios describing various fertigation regimes were defined, and a technique for the generation of set points for water and nutrient application on the basis of pre-defined optimisation goals was developed. These goals included drainage volume and nutrient concentration, nutrient application rate, fruit dry matter concentration, and fruit growth rate.The overall system was evaluated in a greenhouse experiment. In comparison with simulated 'normal' cultivation, optimisation of water and nutrient application indeed resulted in reduced application and drainage rates, increased fruit growth rate, and a dry matter concentration that met the optimisation goal. In conclusion, the monitoring and control system offers good prospects for efficient control of water and nutrient use, and control of crop growth in future control of greenhouse cropping systems. INTRODUCTIONCommon horticultural practice is to couple application of nutrients and water. Nutrient composition of the drain and substrate solution is usually analysed in an external laboratory every fortnight, on the basis of which the nutrient concentrations in the nutrient solutions are determined. During the next two weeks, recirculated drain and nutrient solutions are mixed until a certain electrical conductivity (EC) is reached. If the Na concentration in the drain reaches unacceptably high levels, drain is sluiced to the surrounding surface water. Increased crop transpiration leads to increased water and nutrient application. Applied nutrient quantities therefore usually exceed the needs of the crop. Moreover, possibilities to control crop growth and product quality by a regulated water and nutrient supply are not used by the growers. This approach leads to excess use of water and nutrients and their emission to the surrounding environment. The obvious solution is to supply water and nutrients based on the needs of the crop at each particular moment, which varies according to environmental conditions and crop development.Those issues were addressed in the 'Hydrion-Line' project. The basic principle

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