Deliverable 6. Models for salt accumulation in recirculating nutrient solution culture (UNIPI)

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In closed-loop hydroponics a complete nutrient solution is prepared with water that generally contains non-essential ions, and recirculated until chemical characteristics (namely EC and the concentration of potentially-harmful ions) are below a given threshold that is dependent on many factors, first of all on the crop’s tolerance to salinity.

Tipically, when poor-quality irrigation water is used, there is a rapid increase in EC due to the accumulation of ions such as sodium, chloride, and sulphate and, in case of hard water, calcium and magnesium. Bicarbonate ions, which are often contained in underground water, are neutralised by acid injection for pH control and do not represent a relevant problem. Instead, micronutrients, such as B or heavy metals, may accumulate to toxic levels; however, their concentrations are in order of micromoles per litre and, at variance with other ions that can be indirectly determined by measuring EC, these ions have to be monitored through expensive and time-consuming laboratory analysis.

A simple mathematical model is proposed to estimate how fast the concentration of a given ion increases or decreases in dependence on the relevant factors that influence plant mineral relations in closed-loop hydroponics.