Improving the control of sodium accumulation in closed-loop soilless culture systems using ion selective electrodes and the DSS NUTRISENSE

The management of sodium accumulation in the recycled drainage solution (DS) is a major challenge in closed-loop soilless culture systems (CLS). Currently, this problem is addressed through complete or periodic discharge of the DS. An attractive alternative approach is to compensate for sodium accumulation by reducing the concentrations of macronutrients in the DS, thus maintaining a target electrical conductivity without or with minimal DS discharge.
By employing ion selective electrodes (ISEs) to directly measure macronutrient concentrations in the DS, this strategy can be much more effectively implemented, as the risk of nutrient depletion is minimised.
To evaluate the efficiency of the new strategy and the performance of the ISEs, an experiment with cucumber crop and three treatments was conducted.
The plants were grown in one open soilless system and one CLS, with standard nutrient management and one CLS were the new strategy in salinity management was applied.
The irrigation water had 2.5 mM of Na⁺. In the control CLS, a NS with a standard composition was supplied throughout the cropping period.
In the ISE treatment, the NO₃^–, K⁺, Ca²⁺, and Na⁺ concentrations in the DS were daily measured using LAQUAtwin ISEs (Horiba, Kyoto, Japan), while EC and pH were also daily measured using portable instruments, and Mg²⁺ and SO₄^2- were calculated using the measured data.
The data obtained from these measurements were subsequently introduced into NUTRISENSE to calculate a readjusted NS composition and the injection rates of single-salt fertilisers that are necessary for its implementation.
The LAQUAtwin ISEs proved to be highly accurate and the measured EC, pH, NO₃^–, K⁺, Ca²⁺ and Mg²⁺ concentrations in the DS were maintained close to the readjusted target values.
The results show that the strategy to reduce the nutrient concentrations in the root zone to compensate for sodium accumulation by daily readjusting the supplied NS composition using data from ISE measurements, is efficient and scalable for commercial application.

I International Symposium on Protected Cultivation, Nettings and Screens for Mild Climates

E. Giannothanasis, M. Tzouganakis, T. Ntanasi, I. Karavidas, K. Argyropoulou, G. Ntatsi, R.B. Thompson, D. Savvas

cucumber, salinity, hydroponics, nutrient recirculation, nutrient management

https://doi.org/10.17660/ActaHortic.2025.1437.42