INFLUENCE OF pH ON THE YIELD OF PLANTS IN AQUAPONIC SYSTEMS

Abstract

An important aspect of aquaponic systems is the balance between fish, microorganisms and plants, which is ensured by optimal environmental conditions, in particular the pH level. The authors note that fish in such systems release a large amount of nitrogen waste, which after nitrification becomes available for absorption by plants. However, the increased content of ammonium (NH4+) that occurs at high pH levels can be toxic to plants and negatively affect yield. Research was conducted on an aquaponic system with catfish clary and Lactuca sativa Batavia Aficion lettuce. Plants were grown at two pH levels (6.5 and 7.0), which made it possible to compare their growth, biomass accumulation, and chemical composition. The results showed that lowering the pH to 6.5 helps to increase the yield of lettuce: fresh shoot biomass by 277.9 g at pH 6.5 compared to 270.9 g at pH 7.0. The weight of dry biomass at pH 6.5 is also higher than at pH 7.0. It was observed that decreasing the pH also affects the concentration of trace elements, in particular, the accumulation of manganese increased at pH 6.5, while the zinc content was higher at pH 7.0. In addition to the study of plant indicators, the effect of pH on nitrification was analyzed – the process of converting ammonium into nitrates, which is an important element in supplying plants with nitrogen. Studies have shown that at a pH below 6.5, the activity of nitrifying bacteria decreases, which can lead to ammonium accumulation in the water and toxic conditions for fish. To maintain the balance between nitrification and plant productivity, it is recommended to maintain a pH level of about 6.5–7.0, which provides optimal conditions for the development of both plants and microorganisms. Lowering the pH to 6.5 helps to increase lettuce biomass and improve nutrient absorption, while increased pH can negatively affect the availability of important elements and reduce the efficiency of nitrogen metabolism. The results of this research have important practical significance for optimizing the conditions for growing plants in aquaponic systems, which will increase their yield and stability.