Nutrient cycling in aquaponics systems

In aquaponics, nutrients originate mainly from the fish feed and water
inputs in the system. A substantial part of the feed is ingested by the fish and either
used for growth and metabolism or excreted as soluble and solid faeces, while the
rest of any uneaten feed decays in the tanks. While the soluble excretions are readily
available for the plants, the solid faeces need to be mineralised by microorganisms in
order for its nutrient content to be available for plant uptake. It is thus more
challenging to control the available nutrient concentrations in aquaponics than in
hydroponics. Furthermore, many factors, amongst others pH, temperature and light
intensity, influence the nutrient availability and plant uptake. Until today, most
studies have focused on the nitrogen and phosphorus cycles. However, to ensure
good crop yields, it is necessary to provide the plants with sufficient levels of all key
nutrients. It is therefore essential to better understand and control nutrient cycles in
aquaponics.