Introduction
Under the new Commission Regulation (EU) 2018/848, which has entered into law in January 2022, aquaponic produce cannot be certified as organic in the European Union. Given the multiple components of an aquaponic system, which involve growing plants in hydroponic conditions, recycling of fish waste, and raising fish in artificial conditions, the achievement of organic certification for aquaponic produce is a complex matter dictated by many parameters. In the EU, aquaponics is considered a type of hydroponics, and mainly because of the lack of soil in its systems it is excluded from organic certification. This exclusion is considered to hinder the development of aquaponics, as it makes it difficult for producers to increase their earnings and effectively market their products. The research undertaken explores ways through which different soil substrates and potting mixes can be included in coupled and de-coupled aquaponics, and aims at helping aquaponics with its marketability, commercialisation, public acceptance, and popularity by bringing the technology one step close to organic certification. The research was done through nine different experiments, which took place between April 2021 and August 2022. The experiments aimed at investigating the effects that soil has on the health, growth, and quality of the plants and the fish, whilst examining how the soil microbiome is affected by the use of aquaponic water and processed sludge. This presentation will include the results and conclusions from all the experiments. The experiments are listed below, with a short overview for each.
Experiment 1: Coupled aquaponics of Basil and Nile tilapia #1
This experiment investigated the effects of aquaponic water on the growth and quality of basil (Ocimum basilicum), as well as potential effects of soil addition to fish health. The plants were grown in soil-filled pots placed in trays on top of fish tanks, creating full-recirculation, coupled aquaponic systems. The growth of the plants in soil-based aquaponic systems was compared to that of conventional, soil-less aquaponics. Two types of soil potting mixes were used, one with compost, and one without. The design of the systems was inspired by conventional coupled aquaponics, however the plant units were designed to allow the plant roots in soil-filled pots continuous access to fish water.
Experiment 2: Coupled aquaponics of Basil and Nile tilapia #2
This experiment was a continuation of the previous one, with a few modifications: compost amount was reduced, and the soil-less treatment was substituted by another soil-based treatment.
Experiment 3: De-coupled aquaponics of Basil in pots
This experiment investigated the effects of aquaponic water and processed sludge on plant growth and quality and soil microbiome in basil (Ocimum basilicum) cultivated in pots. The effects of the use of the different substrates and water type on plant health, quality, growth, as well as soil microbiome composition were investigated.
Experiment 4: De-coupled aquaponics of Onions in raised beds
This experiment investigated the effect of watering onions (Allium cepa) cultivated in raised beds and watered with water from different sources; the aims of the study were to compare the effects of manure, currently allowed in organic production, and fish effluents used as fertilisers on the growth and quality of the plants, and to investigate the effects of the different fertilisation regimes on the soil microbiome composition. Four outside raised beds were divided into four sub-units, and each subunit was devoted to the cultivation of onion sets. The four treatments were the following: onions watered with tap water, onions supplied with horse manure and watered with tap water, onions watered with aquaponic water, and onions watered with aquaponic water with sludge.
Experiment 5: De-coupled aquaponics of Bok Choy in certified topsoil
This experiment investigated the effect of watering bok choy (Brassica rapa subsp. chinensis) cultivated in detached containers in UK-certified topsoil and watered with water from different sources. The aim of the study was to compare the effects of manure, currently allowed in organic production, and fish effluents used as fertilisers on the growth and quality of the plants. The four treatments, each replicated four times, were the following: plants watered with tap water, plants supplied with horse manure and watered with tap water, plants watered with aquaponic water, and plants watered with aquaponic water and sludge.
Experiment 6: De-coupled aquaponics of Turnip in certified topsoil
This experiment investigated the effect of watering turnip (Brassica rapa subsp. rapa) cultivated in detached containers in UK-certified topsoil and watered with water from different sources. The methodology followed was identical to the methodology of experiment 5.
Experiment 7: Use of Barley for nutrient uptake of soil treated with fish effluents
This experiment investigated the use of barley (Hordeum vulgare) grown in the same raised beds where the onions from experiment 4 grew, in order to measure the uptake and retention of nutrients that would otherwise be washed off by rain by a cover crop.
Experiment 8: Coupled aquaponics of Chilli peppers and Nile tilapia
This experiment investigated the effects of aquaponic water on the growth and quality of chilli peppers (Capsicum annuum) grown in soil-filled pots, placed in trays on top of fish tanks, creating full-recirculation, coupled aquaponic systems. Two types of soil potting mixes were used, one with compost, and one without.
Experiment 9: De-coupled aquaponics of Chilli peppers in pots
This experiment investigated the effects of aquaponic water and processed sludge on plant growth in chilli peppers (Capsicum annuum) cultivated in pots. The effects of the use of the different substrates and water type on plant health and growth, and fruit quality were investigated.