Developing and validating a modelling approach linked with ion selective electrodes to control pollution of water resources from greenhouse crops

The recycling of drainage solution (DS) in greenhouses by applying closed-loop soilless cropping systems (CLS) eliminates pollution of aquifers by nitrogen and phosphorus emissions. However, the variable nutrient composition of the DS poses a significant challenge to its recycling in CLS. To addresses this challenge, a strategy was developed, based on daily monitoring of macronutrient concentrations in the DS using ion-selective electrodes (ISE) coupled with a modelling approach applied through a decision support system (DSS). The ISE measurements were input data for the DSS to calculate appropriate rates of different single-fertiliser concentrated solutions for automatic injection into a mixture of DS and raw water. The fertiliser injection rates were transmitted online to a fertigation system equipped with nine different single-fertiliser concentrated solutions and were applied automatically in real time. The objective was to maintain the root-zone nutrient concentrations within an optimal range. To test this technology and to validate the modelling approach applied through this DSS, tomato was grown in a CLS with daily measurement of NO₃⁻, K⁺, Ca²⁺, and Na⁺ concentrations in the DS using ISEs. The accuracy of the ISEs was confirmed by comparing their measurements with those from standard laboratory procedures in the same samples. The model approach successfully maintained the target nutrient concentrations in the root zone and increased fruit yield by 7.6 % and the agronomic efficiency of nitrogen by 23 %. The proposed technology is expected to encourage the adoption of CLS by growers thus minimising environmental impacts from greenhouse crops.