The potential of becoming one of the most effective sustainable production systems for the combined production of animal protein and plant crops is attributed to decoupled aquaponic systems (Kloas et al. 2015, Monsees et al. 2017). Here, recirculating aquaculture systems for fish production are combined with hydroponic systems for soilless plant production allowing individual management of each single compartment thereby recycling dissolved nutrients derived from metabolism of the fish. Nevertheless, professional adjustment of selective micro- and macro-nutrients can be very expensive, especially for small to medium aquaponic operations (e.g. complete lab analysis of RAS-derived water). Therefore, (i) one of the aims of this study is to provide cost effective strategies for nutrient management in aquaponics systems. In order to meet specific plant requirements, the knowledge on nutrient concentrations as well as predictable patterns and trends in the RAS water is pertinent for correct fertilizer addition. Consequently, further aims are to (ii) identify the origins of macro- and micro-nutrient and to find accumulation patters, as well as the attempt to predict their general trends, and nutrient dynamics (N,P,K), (iii) to meet plant needs as close as possible according to a professional fertilizer management in hydroponic production units.
Material & methods
Literature values from RAS and aquaponic applications were collected with regard to predefined boundary conditions. Additionally, water samples were collected from different research or commercial RAS or corresponding aquaponic facilities. Micro- and macro-nutrients were analyzed using continuous flow analysis (CFA) and inductively coupled plasma-optical emission spectrometry (ICP-OES). Models were tested in a first trial with two different treatments against a hydroponic control (n = 3, 10 lettuce plants per replicate).
General nutrient patters for RAS and aquaponic facilities were identified and used for the development of models. The first results of the model testing in a hydroponic setup revealed that lettuce can be effectively produced in an aquaponic setup without the need for detailed nutrient analyses. The lettuce growth was comparable between both aquaponic applications, but significantly reduced by 10 % compared to the hydroponic control (Fig. 1).
The potential of identifying and using nutrient patterns in RAS and aquaponics for a combined production of fish and plants in a decoupled aquaponic approach were clearly shown in this study. By applying this easy approach, professional nutrient management can be simplified for small and medium aquaponic producers. The first results are very promising, showing that overall aquaponic yield is not affected with respect to the type of nutrient management. The post adjustment of the nutrient profile using fish water for professional hydroponic application was more challenging as in conventional hydroponics (with rain water or tap water) but it was demonstrated that for most nutrients the set points were reasonably close to the recommended nutrient concentrations as it was also shown in other studies (Suhl et al. 2016, Monsees et al 2019).
Additionally, the authors are very optimistic that with ongoing professionalization and standardization of practices in decoupled aquaponic technology, more farmers will adapt towards professional management approaches and that comparable yields to conventional hydroponic production can be expected, as it was already show e.g. in Monsees et al. 2019
Kloas W, Groß R, Baganz D, Graupner J, Monsees H, Schmidt U, Staaks G, Suhl J, Wittstock B, Wuertz S, Zikova A, Rennert B (2015) A new concept for aquaponic systems to improve sustainability, increase productivity, and reduce environmental impacts. Aquaculture Environment Interactions, 7 (2) 179-192
Monsees, H, Suhl, J., Paul, M., Kloas, W., Dannehl, D., Wuertz, S. (2019). Lettuce (Lactuca sativa, variety Salanova) production in decoupled aquaponic systems: Same yield and similar quality as in conventional hydroponic systems but drastically reduced greenhouse gas emissions by saving inorganic fertilizer. PloS one, 14(6), e0218368
Monsees, H., Kloas, W., & Wuertz, S. (2017). Decoupled systems on trial: Eliminating bottlenecks to improve aquaponic processes. PloS one, 12(9), e0183056.
Suhl J, Dannehl D, Kloas W, Baganz D, Jobs S, Scheibe G, Schmidt U (2016). Advanced aquaponics: Evaluation of intensive tomato production in aquaponics vs. conventional hydroponics. Agricultural water management, 178, 335-344.