TOMATO PRODUCTION IN AQUAPONIC SYSTEM: MASS BALANCE AND NUTRIENT RECYCLING

Zala Schmautz*1, Andreas Graber1, Alex Mathis1, Tjaša Griessler Bulc2 and Ranka Junge1
 
1 Zurich University of Applied Sciences, Institute Natural Resource Sciences, Grüental, 8820 Wädenswil (Switzerland), E-mail: ranka.junge@zhaw.ch
2 University of Ljubljana, Faculty of Health Sciences, Ljubljana (Slovenia)

Introduction

Besides being essential to life, food also forms part of cultural identity and plays an important role in the economy. While people know that food is affecting their health, they are usually not aware that its production, transport, storage and consumption have a negative impact on the world's natural resources (European Commission, 2014). Currently, agriculture uses more than 70% of world's freshwater resources (FAO, 2004). Due to the increasing demand for food because of population growth and the need to save freshwater, the efficiency of food production has to be increased. Aquaponic, the combination of hydroponics with aquaculture, is one of the most promising sustainable systems for food production (Carlsson, 2013). It has a little environmental impact because of its low water consumption (Licamele, 2009; Endut et al., 2011). The main concept of the aquaponic system is to balance the nutrients in the system (Licamele, 2009). Normally, aquaculture effluents contain sufficient levels of nitrogen (N), phosphorous (P), and other secondary nutrients and micronutrients such as boron (B) and copper (Cu) (Diver, 2000), while levels of potassium (K), calcium (Ca), and iron (Fe) are generally insufficient (Seawright et al., 1998; Rakocy et al., 2006). There are a few studies that allow complete budgeting on the nutrients. Often the studies which include complete budgeting were done on a very small scale (Seawright et al., 1998; Rafiee and Saad, 2005), or only very few nutrients were budgeted at all (Adler, 1998; Graber and Junge, 2009; Endut et al., 2011).

Materials & Methods

Three identical experimental aquaponic systems (4.7m3) were installed in a foliar greenhouse at the Zurich University of Applied Sciences Campus in Wädenswil, Switzerland. Each  system was composed of a fish holding tank, solids removal unit, solids thickening unit, moving bed biofilter, oxygenation cone, three different hydroponic sub-systems (NFT channel, floating raft culture, and a drip irrigation system), and collection sump. In spring 2014, the "Wädenswil" aquaponic system was stocked with Gardenberry tomatoes (Lycopersicon lycopersicum) and Nile tilapia (Oreochromis niloticus). The primary inputs (fish feed, nutrient supplementation for the hydroponic part, and fresh water) and outputs (tomato fruits, green biomass, root biomass, sludge, and fish biomass) of the aquaponic system were taken into the calculation to determine the nutrient balance. For the estimation of the nutrient distribution (e.g. carbon (C), N, P, K, Ca, magnesium (Mg), Fe, manganese (Mn), zinc (Zn), and Cu) for mass balance, data from 12 June 2014 to 5 November 2014 was used. The sample nutrient content was measured with axial inductively coupled plasma and CHNSO analyser. Based on this, the nutrient balance of the system was determined. The nutrient content of the system water was measured weekly with rapid chemical tests (Hach-Lange) and spectrophotometer.

Results

In the balance of the entire aquaponic system, fish feed provided most of C, N, and Cu (>90%). Aquaculture effluents contained high levels of C, N, P, and Cu, whereas the levels of K, Ca, and Fe provided only by fish feed, were found to be insufficient. K was mainly provided by nutrient supplementation (75%) while P was mainly provided by fish feed (72%). Input of Fe was provided by nutrient supplements (51%) and fish feed (45%). Results showed that the distribution of nutrients differed in different parts of the aquaponic system. C, N, P were mainly accumulated in tomato fruits (39% C, 16% N, 32% P) and fish mass (28% C, 66% N, 28% P). K was mainly accumulated in tomato fruits (47%) and green biomass (32%). Ca was mainly accumulated in green biomass (56%) and roots (39%). According to the mass balance, the calculated amount of macronutrients was highest in the fish and the amount of micronutrients highest in the tomato plants.

Conclusion

Balancing the nutrient load of the system with the density of the fish, feeding rate, and nutrient requirements of the plants, lead to optimization and better productivity of the system (Licamele, 2009). When balancing the system, some losses in the mass balance were detected. Most of these could probably be explained by insufficiently detailed data on fish biomass and sludge samples. The aquaponic systems required an average daily water addition of 1.6% of total system volume from 12 June to 5 November 2014. To our knowledge, this study was the first attempt to nearly complete budgeting of a wide array of nutrients. However, further research on its efficiency and performance should be made.

References

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