Response of Tomato (Solanum lycopersicum L.) Varieties to Electrical Conductivity Modulation in a Recirculating Hydroponic System

Abstract

Tomato production in tropical countries, including Ghana, has remained low, threatening sustainable food security and nutrition. The demand for the produce far exceeds its supply, and this imbalance is expected to worsen as the population grows, and the impacts of climate change intensify. Tomato yields in Ghana have remained low despite the adoption of greenhouse systems, unlike in some developed countries. To bridge this production gap and improve sustainable productivity, efficient and adaptable technologies are required. One promising approach is the use of a low-substrate-volume hydroponic system with high-density planting, coupled with low-node order pinching. There is limited information on how nutrient solution electrical conductivity (EC) modulation affects tomato performance in this system. This study aimed to evaluate the effect of nutrient solution EC modulation on the physio morphological, yield, fruit quality and water use efficiency responses of tomatoes. The study was conducted in the greenhouse at the University of Ghana's Forest and Horticultural Crops Research Centre (FOHCREC), Kade. Four EC modulation treatments were tested: high, low, high-low, and low-high. Plants in the high-low and low-high treatments received high or low EC during the vegetative stage and then switched to the reverse EC level during the reproductive stage. Two tomato varieties, Anna and Jaguar, were evaluated across these treatments. Two experiments, which followed a 2 x 4 factorial in a randomized complete block design, with three replications were conducted. The results showed that EC modulation significantly affected plant height, leaf number, and stem diameter, with variety Anna displaying greater height (30.3% to 38.1% higher) under high EC. High EC also promoted greater stem girth. Both varieties showed changes in photosynthetic efficiency and chlorophyll content, with Anna having higher chlorophyll levels at high EC, while Jaguar maintained stable chlorophyll content across EC modulations. Water use efficiency (WUE) was higher in high or high-low EC treatments, with Jaguar exhibiting superior WUE compared to Anna. Yield and fruit quality were also influenced by EC modulation. Anna had consistent fruit numbers across EC treatments, while Jaguar's fruit number decreased under high EC. However, Jaguar produced 36.7% to 45.3% higher yields than Anna. Anna had higher lycopene, vitamin C, and total soluble solids under high EC, while Jaguar exhibited less variation. Both varieties showed an increase in fruit pH with high EC. The study suggests that Anna is more stable under variable EC conditions and offers better nutritional content under high-low EC modulation, while Jaguar was better in water-use efficiency and yield, particularly under high or high-low EC. Achieving high yield, fruit quality, and resource efficiency depends on both nutrient solution EC levels and variety selection.