– Usually, various sorts of material accumulate under fish cages: feed residues, pharmaceutical residues, fish droppings – all that settles on the bottom. Fish farms are obliged to clean these sediments from water bodies. Then, they need to be disposed of. One environmentally efficient method could be placing the wastes on farmlands. The point is that the sediments contain mineral nutrients that could potentially be useful as a partial substitute for fertilizers. Above all, they are rich in phosphorus, and phosphate fertilizers are widely used in our region, – explained Elena Ikkonen, Senior Researcher at the Laboratory of Plant Ecophysiology, Institute of Biology KarRC RAS.
During the experiment, a special substrate was prepared and allowed to mature. It was sediments from a trout farm mixed with peat soil in different proportions – 0:1, 1:10, 1:7, 1:5. Then, 'Medvezhye Ushko' cv. lettuce was planted in pots filled with the substrate. The pots were placed in a greenhouse, where the plants were grown under natural light, temperature, and photoperiod with regular watering. After 37 days, the plants were harvested to determine their parameters. Prior to this, the sediments, soil, and plants were assayed for heavy metal content.
At the start of the experiment. Photo: E. Ikkonen / Institute of Biology KarRC RAS
The study did not reveal any harmful effects of aquaculture sediments on soil properties or lettuce growth. The scientists attribute this to the low total content of heavy metals and the high concentration of phosphorus in the sediments. Moreover, the addition of sediments increased the soil content of vanadium, which is beneficial for plants, and reduced the content of manganese, thereby lowering decreasing its toxic load. As for lettuce productivity, the fertilizer had a neutral rather than positive or negative effect, but some structural changes were observed in the leaves, leading to an increase in the leaf area index. It is also possible that the sediments can improve the physical properties of the soil – its aeration, water and thermal conductivity, and water-holding capacity – and thereby exert a beneficial effect on plants. This hypothesis requires further study. Additionally, the long-term effects of sediment use need to be investigated.
– Since the main objective of this experiment was to assess whether sediments from fish cages could be detrimental to soil or plants, we chose relatively fertile soil, which did not require extra fertilization. So, it is too early to draw definitive conclusions about the possibility of replacing the main fertilizers with aquaculture wastes. In the next experimental stage, the soil will be a poorer, sandy type, and we will assess how useful the sediments are specifically as partial replacement for fertilizers, – shared Elena Ikkonen.
Structural changes in leaves resulted in an increased leaf-area index. Photo: E. Ikkonen / Institute of Biology KarRC RAS
The results of this study were published in the international journal Eurasian Soil Science.
“The study revealed no hindrances to using aquaculture sediments from water bodies of northwestern Russia on farmlands. Furthermore, they can be a potentially suitable substrate for green agriculture”, – concluded the authors of the article.
The research is conducted within the project «Prospects of using sediments from fish farms in northern regions of Russia to increase soil fertility and crop yields», supported by the Russian Science Foundation.
– Our research results demonstrate the potential of sediments from fish farms as a partial substitute for expensive fertilizers, and underpin a positive view on the possibility of recycling them without harming the environment, – noted the project leader, RAS Corresponding Fellow Olga Bakhmet.
The study participants examined also the effect of sediments from fish farms on seed germination and seedling parameters in oats, rye, radish, and peas – including root length, height, and mass. According to Lyubov Evstratova, Chief Researcher of the Vilga Agrotechnology Laboratory at the KarRC RAS Department for Multidisciplinary Research, the application of sediments with elevated potassium and calcium content promoted the germination and sprouting rates. "Cereals and radish were more responsive to the treatment than legumes. For example, laboratory seed germination in oilseed radish was promoted by the original and water-diluted sediments by 10.5% and 12.2%, respectively. We also observed a stimulation of root growth and accelerated sprouting”, – the scientist remarked.
"A promising solution for mitigating the negative impact on the north-boreal lake ecosystems of Karelia from the accumulation of sediments containing natural nutrients and aquaculture wastes would be to use them as organic fertilizers in agriculture", – summarized the authors of the paper published in the journal Vestnik of the Russian Agricultural Science.
