Tomato Productivity and Quality in Aquaponics: Comparison of Three Hydroponic Methods
Zala Schmautz, Fionna Loeu, Frank Liebisch, Andreas Graber, Alex Mathis, Tjaša Griessler Bulc, Ranka Junge
2016
Water
Aquaponics (AP) is a food production system that combines hydroponic (HP) crop production with recirculating aquaculture. Different types of hydroponic systems have been used for growing crops in aquaponics. However, very few studies have compared their suitability and efficiency in an aquaponic context. The study presented here compares tomato yield, morphological (external) and biochemical (internal) fruit quality, and overall tomato plant vitality from three different HP systems (nutrient
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... m technique, drip irrigation system, and floating raft culture) and examines the distribution of nutrients in different parts of the tomato plant. Three replicate AP systems were set up, each incorporating the three different HP systems coupled with a separate recirculating aquaculture unit growing Nile tilapia. The results showed that the choice of the cultivation system had little influence on most of the above-mentioned properties. Tomato fruit mineral content was found to be in similar range for N, P, K, Ca, Mg, Fe, and Zn as reported in the literature. Yield and fruit quality were similar in all three systems. However, the drip irrigation system did perform slightly better. The slightly higher oxygen radical absorbance capacity (ORAC) of the fruits grown in AP in comparison to commercially produced and supermarket derived tomatoes might indicate a potential for producing fruits with higher health value for humans. staple foods to meet caloric demand, but also the challenge of producing a wide variety of high quality foods with good nutritional properties. Therefore, it is important to find sustainable food production systems which can also be maintained within settlements or cities. Aquaponics (AP) is one of the most promising sustainable systems for food production that combines hydroponic systems (HP) with recirculating aquaculture systems (RAS). It has the potential to play a major role in food provision and tackling global challenges such as water scarcity, food security, water pollution, high energy use and excessive food transport miles [5] . If AP is operated in a closed water loop, it has little environmental impact because the food is produced with low water consumption [6, 7] . Plant production yields in AP have been reported to be higher than for crops grown in soil [8, 9] , however data are scarce. In AP, nutrients enter the system in the form of fish feed. The feed is ingested and metabolized by the fish. The remains of the feed and the metabolic products from the fish dissolve in the water creating an aquaculture effluent that provides most of the nutrients required for plant growth in a HP part of the system. Microorganisms in the biofilter, on plant roots, and in the recirculating water release and convert the nutrients (e.g., phosphates from the debris, and ammonium to nitrate) and the plants assimilate them, thus treating the water, which flows back to the aquaculture component of the system [5, 8] . In AP, fish, plants, and bacteria coexist in the same water, albeit in different compartments of the system [10]. Different types of HP systems have been used for growing crops in AP: (i) drip irrigation; (ii) floating raft culture; (iii) gravel bed; and (iv) nutrient film technique (NFT) [5] [6] [7] [8] [11] [12] [13] [14] , however very few studies have compared different HP production systems in an AP context. The only paper we are aware of is by Lennard and Leonard [15] compares floating rafts, gravel beds, and NFT for growing lettuce in AP and found that NFT produced significantly less biomass and removed the nutrients from fish water less efficiently than the other two systems. Generally, all plant species that can be adapted to growth in HP systems can also be grown in AP [16] , meaning there is an extremely wide variety of choices. Savidov [17] reported growing over 60 different types of plant species in AP. Lettuce, specialty greens and herbs (chives, basil, spinach, and watercress) have low to medium nutritional requirements and are well adapted to AP [16] . Fruit yielding plants (tomato, bell pepper, cucumber, and squash) have a higher nutritional demand and perform better in heavily stocked AP systems. In indoor systems, the most commonly used tomatoes are greenhouse varieties which are better adapted than field cultivars to low light and high humidity conditions [16] . According to FAOstat [18], tomatoes are worldwide the second most important vegetable crop after potatoes. Tomatoes are rich in nutrients and vitamins which are associated with healthy food, i.e., carotenoids, flavonoids and lycopene [19, 20] . Leaf nutrient concentrations can be used to detect the mineral nutritional status of the plants and thus might help to reveal differences in nutrient availability in different growing systems, whereas fruit nutrient content indicates the nutritional value for human consumption [21] . Graber and Junge [5] compared four varieties of tomatoes (Grapella, Rose of Berne, Frog King Golden Orb, and Sweet from Hungary) in AP, and in commercial HP cultivation with applications of mineral fertilizer according to Resh [22]. They found that all varieties performed better in AP. The purpose of this study was to compare tomato yields, morphological (external) and biochemical (internal) quality, and overall plant vitality in three different HP systems (NFT system, drip irrigation system, and floating raft culture). In addition, nutrient uptake and distribution within the tomato plants was also to be determined.
doi:10.3390/w8110533
fatcat:2ia2mdpdvvanpajouyatklbbaq