Brackish water aquaponics is a promising food production technology that seeks to use plant nutrient uptake to manage wastewater from brackish aquaculture.Adoption of brackish water aquaponics is limited due to salt-sensitivity of common horticultural crops. Improving the salt tolerance of high-value greenhouse vegetables may increase the economic viability and adoption of brackish water aquaponics. The objective of this study was to evaluate the viability of a substrate-based split-root hydroponics system for mitigating salinity stress of tomatoes grown at brackish water salinity levels in a hydroponic system.
Tomatoes were grown in a Dutch bucket perlite system in which each plant’s root systems were partitioned into two separate zones. One root zone was supplied with nutrients containing the salinity treatments (0, 4.5 ppt, and 9 ppt added salinity) while the other received only freshwater. Plants were grown in a randomized, complete block design under controlled greenhouse conditions. Growth metrics (height, width, stem diameter), plant health indicators (SPAD, Yield, trimmed weight), and water quality measurements (pH, EC, and Ion Concentrations) were measured weekly for the duration of the trial starting September 24th, 2025.
Initial results seen from the first official trial show that treatment x time has shown significant interaction over multiple of the observed data points, with most of the differences occurring late in the production cycle. Plant size index showed no differences until week 8 and from then on plants in the control group were larger than those in the medium- and high-salinity treatments. The increased size did not lead to differences in either fruit count or fruit yield. In general, salinity did not affect other growth and development measurements.
The differences in growth measured after week 8 may indicate the accumulating effect of salinity stress on the tomato plants. However, the lack of yield differences up to week 10 is a positive sign that split-root systems are effective, at least in the short term, at mitigating salinity stress. We hypothesize that providing fresh water to part of the root system allows for more water uptake, hence protection against osmotic stress that is common under high-salinity conditions. In future studies, we will explore the effects of irrigation timing and volume of both freshwater and salinity treatments on growth and yield of tomatoes.