Friday, 2 February 2018

Aquaponic Nutrients and the impact on Plant Production

Boris Delaide (University of Liège, BE) gave a presentation of his recent study of nutrients in aquaponics and their impact on lettuce production. Here are some key takeaways.

Aquaponics has a much lower level of nutrients than a typical hydroponic system, yet produces the same amount of lettuce

Most of the nutrient was lost due to the water changes and the sludge removal (solid fish waste removed from the system). Aquaponic systems need to take advantage of the nutrients locked in the sludge. Adding a digester to mineralize the solids is a good place to start.
Despite all of this, Aquaponics is as productive as an optimized hydroponic system with a much higher concentration of nutrients. This echoes the findings of others such as Nick Savidov.

His hypothesis is that aquaponics performs as well as hydroponics despite having less nutrients because of the microflora in the rhizosphere which help the roots in absorbing nutrients more efficiently. The second reason may be the dissolved organic matter may be feeding the plants directly or promoting the uptake of nutrients.
He also found that if the nutrients in the aquaponic system were supplemented so that they were equivalent to the hydroponic system, the plants would grow at a much faster rate than the hydroponic system.

Aquaponic solution supplemented with nutrients equalling what would be found in a typical hydroponic system, produced 39% more plant mass than the hydroponic system. This is due to the more efficient uptake of nutrients in the aquaponic solution.
Finally, he looked at different methods of digesting the sludge to release the nutrients that were locked in the solids. More work needs to be done in this area, but it is promising.

Here is the full presentation:

Download the study here

1 comment:

  1. I have read the published paper on this work. if you read it carefully, you will see that actual aquaponic systems were NOT tested. Rather, water was removed from a RAS and this was 1/ used as an aquaponic analogue (questionable method) and 2/ supplemented with hydroponic nutrients to match hydroponic solution nutrient strengths. Both test solutions were compared to a standard hydroponic control. The tests ran for about 3-4 weeks. Therefore, there was no actual comparison of a TRUE aquaponic system to a hydroponic system or an aquaculture system! Just water removed from a RAS and supplemented in one test case. I think some of the assumptions made about the results of these trials are questionable because in essence, the paper actually argues that the supplemented RAS solution represents an advanced de-coupled approach and the RAS solution represents a true recirculating aquaponic approach. The point of the paper is to argue therefore, that the de-coupled approach is better than a traditional fully recirculating approach. Its all very questionable from a scientific point of view! Wilson


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