Oxygen within the root zone is an important requirement to keep roots alive for enhanced nutrient uptake and plant growth. In water-based systems, oxygen of the water is maintained by blowing air through the water with the aid of diffusers or air stones . Where aeration is not maintained, di ssolved oxygen (DO) concentration (mg/l) reduces . At very low DO, water quality parameters such as nitrates, pH, and electrical conductivity (EC) are greatly affected. These changes affect plant growth and productivity. The objectives of this study were to 1) compare water quality of two nutrient sources in response to aeration and no aeration, 2) to assess the growth, stomata conductance, SPAD and yield of Romain lettuce in the systems. The experiment was a 2x2 factorial arrangement in a randomized completed block design with four replicates. The results indicate that n o aeration led to a reduction in DO level in both aquaponics and hydroponics systems (1.12 mg/l and 3.46 mg/l respectively). No a eration caused no statistically significant change in EC for either system but led to 70 mg/l reduction in nitrate than aeration in aquaponics. Additionally, n o aeration led to a 1 o C increase in temperature than the aerated for both systems but decrease in pH by 1 unit in only aquaponics system. Generally, plant height decreased in no aeration across systems whereas a verage SPAD value was higher by 3 units and 1 unit in no aeration than aeration aquaponics and hydroponics respectively. Leaf temperature and stomata conductance showed no statistically significant differences among the treatments. Although root length was statistically different between aeration and no aeration, root dry mass was not. Also, shoot weight per plant was about 50% and 29% more in aeration than no aeration for fresh and dry mass respectively . In conclusion, the study revealed that aquaponics-based system was more affected by a lack of aeration than hydroponics system. Also, no aeration had more effect on productivity related traits than physiological related traits except SPAD of the lettuce plants. It was observed that no aeration reduced tipburn which is a major challenge in hydroponic Romain lettuce production. Therefore, no aeration should be explored further. Future research should introduce an oxygen zone around the root area. This might counter the negative effects of no aeration in deep water culture system.
Key Words : Dissolved oxygen, Electrical conductivity, Stomata conductance, leaf SPAD value, Deep water culture