The initial and the setting of critical limits of EC, Na and Cl in the solution dictate the frequency of discharge from the system. The system constantly monitors the nutrient solution for EC, pH and nutrient concentrations. Nutrients are applied according to factors such as plant requirements, transpiration, and required content of elements in tissue and level of nutrients in the solution. A frequent level of analysis and monitoring of these factors is required to maintain the stability of the system, to save water and nutrients and to achieve maximum yield. Recent European Community directives emphasize the need for growers to reduce their nitrate emission.
Water is a scarce natural resource, but is at a constant total quantity.
This paper describes recirculation systems in greenhouse, their potential savings and the different approaches applied to the nutrient management in such systems. This will allow more circulation and reduce the drainage out of the system. Online EC, pH and nutrient concentration measurement devices are installed at various points in the system to monitor and alter inputs of water, fertilizers and acids. A typical recirculation system is presented in figure 1. The use of rainwater as a diluter when solution's EC builds up is essential.