Development and evaluation of an automated prototype for the fertigation management in a closed system

In France, in order to prevent imbalances and accumulation of nutrients in the plant root zone, most of the soilless crops in glasshouses are cultivated in open drainage systems, which leads to water and fertilizer losses. The goal of the EU project CLOSYS (CLOsed SYStem for water and nutrient management) was to build a prototype which delivers water and nutrients according to the plant needs in a recirculating system. This prototype aimed at controlling production and quality as well as reducing nutrient accumulation or shortage in the root zone in a closed system and avoiding pollution of the environment. This paper deals with the development and the evaluation of the prototype in comparison with a classical closed system for a sweet pepper crop. This prototype includes: substrate and plant models incorporated in an expert system, using substrate and plant sensors, and a real time controller. Technical details and results of each module will be presented. The plant model provided proper simulations of growth and development parameters, nutrient concentrations in the plant organs, plant nutrient and water consumption. The expert system enabled the coupling between plant and substrate models, thus ensuring the system to take into account the weather forecasts. The real time controller managed to control relative water content and electric conductivity in the substrate slabs. A Leaf Area Index sensor was used to calibrate the plant model according to the real crop area development. As a conclusion, the CLOSYS system led to a lower nutrient consumption, lower sodium and chloride accumulation and a proper electric conductivity control in comparison with the classical closed system, while maintaining production and quality.