INFLUENCE OF POTASSIUM SULPHATE ON THE YIELD AND BIOCHEMICAL COMPOSITION OF LEAF LETTUCE IN AN AQUAPONIC SYSTEM

Abstract

The article examines the impact of potassium sulfate (KtSO) supplementation on the yield and biochemical composition of leaf lettuce in aquaponic systems. The study was conducted under two aquaponic conditions: a control line, where plants received nutrients solely from fish waste, and an experimental line, where potassium sulfate was added to the water at a concentration of 0.5 g/dm³. According to the results, lettuce yield in the control line was 2042.74 g/m², while in the experimental line, it reached 3497.7 g/m², which is 71.2% higher. The biomass of plants in the experimental line was also greater, with the maximum plant bundle weight reaching 390 g compared to 340 g in the control. Plant morphology parameters also improved: the maximum plant length in the control line was 53 cm, while in the experimental line, it reached 71 cm. To assess the chemical composition of water, potassium content, ammonium nitrogen, and nitrate nitrogen levels were measured. Nitrate nitrogen analysis showed that its concentration in the control line increased from 9 mg/dm³ to 30.4 mg/dm³, while in the experimental line, it remained at 6.4 mg/dm³. The ammonium ion content decreased to 1.63 mg/dm³ in the experimental line and to 4.53 mg/dm³ in the control line. At the same time, potassium content in the water of the control variant was 8.89 mg/dm³, whereas in the experimental line, it reached 55.2 mg/dm³, indicating the positive effect of potassium sulfate supplementation on the conversion of ammonium nitrogen compounds into nitrate nitrogen and an overall increase in nitrogen uptake by leaf lettuce plants. Chlorophyll content was also measured. In the experimental line, chlorophyll a was 0.79 mg/g, and chlorophyll b was 1.65 mg/g, whereas in the control line, these values were 0.74 mg/g and 1.54 mg/g, respectively. Overall, the results demonstrate the positive effect of potassium sulfate addition on yield, morphometric characteristics, and the chemical composition of leaf lettuce in aquaponic systems.