Automated management of nutrient solutions based on target electrical conductivity, ph, and nutrient concentration ratios

Abstract

An algorithm to automatically formulate the composition and prepare nutrient solutions for soilless cultures based on desired characteristics given as target values is proposed. To formulate the complete ionic composition of a nutrient solution, standard recommendations referring to the following solution characteristics should be available: (i) electrical conductivity (EC), (ii) pH, (iii) concentration ratios of macronutrients (meq basis), and (iv) micronutrient concentrations. Moreover, the mineral composition of the water used to prepare the nutrient solution should be taken into account. To develop the main steps of the algorithm, the total salt concentration (meq L‐¹) of the nutrient solution is related to the desired electrical conductivity. The target pH indicates the concentration of HCO₃ ⁻ in the nutrient solution, whereas the absolute concentration of each macronutrient is derived from the desired concentration ratios and the total salt concentration. The necessary calculations are standardized through the development of formulae. Furthermore, the differences in nutrient concentrations between desired levels in the solution and those found in the tap water represent the amounts of nutrients per volume nutrient solution (meq L⁻¹) which should be added through fertilizers. The above described steps of the algorithm have been tabulated to facilitate their implementation. Moreover, a numerical example concerning the composition of a nutrient solution for cucumbers is given. In the final steps of the algorithm, two standard formulae are used to calculate the quantities of individual macronutrient and micronutrients fertilizers needed to prepare particular volumes of stock solutions. Alternatively, when stock solutions of single fertilizers having known concentrations are used, the composition of the nutrient solution can be automatically adapted to new target values. This task can be performed without replacing the existing stock solutions by rearranging the formulae used in the last steps of the algorithm to calculate dilution ratios instead of fertilizer quantities.