NUTRISENSE: a novel software to automatically control nutrient supply in closed hydroponic crops based either on off-line chemical analyses or on ion-selective electrodes

In closed-loop fertigation systems, the nutrient concentrations in the drainage solution (DS) are variable, and this complicates its recycling because the rates of nutrient injection needed to achieve target concentrations in the supplied nutrient solution cannot be accurately pre-estimated. This problem is further complicated because in commercial horticulture the replenishment process must be performed automatically. To address this problem, a decision support system (DSS) was developed, to automatically calculate nutrient solutions (NS) and re-adjust their composition during the cropping period. This DSS is termed NUTRISENSE and is online available at www.nutrisense.online. NUTRISENSE can automatically calculate the composition of the NS (as kg of each fertilizer for each stock solution in A/B tank systems, or as injection percentages of stock solutions in multi-tank systems) and all additional information needed by the grower to optimize NS supply. Furthermore, NUTRISENSE can be applied during the cropping period to modify the composition of the NS when the plant developmental stage changes, or when results from a chemical analysis of a drainage solution (DS) sample are available. A more efficient approach to overcome the problems arising from the unknown composition of the DS is the online estimation of the nutrient concentrations in the DS using ion selective electrodes (ISE). To apply this alternative, an alternative version of NUTRISENSE was developed, which is used online to control a fertigation system equipped with ISE. The obtained prototype can utilize the online measurements of ISEs to automatically calculate and inject stock solutions of fertilizers needed to prepare NS for closed hydroponic crops. Based on the ISE-measurements, NUTRISENSE calculates in real time the injection rates of fertilizers and control their injection to the mix of DS and irrigation water during the process of drip solution preparation. In the current study, both versions of NUTRISENSE are shortly presented. Furthermore, some data from the application of the internet version of NUTRISENSE in an experimental hydroponic tomato crop are presented.