Aquaponics is a food production technology that combines aquaculture and hydroponics in an integrated recirculating system without soil (Rakocy et al., 2006). The aquaponics ecosystem is composed by fish, bacteria, and plants (Somerville et al., 2014). Fish are fed with dry feed; fish waste is generated by direct excretion into the fish tanks, and organic waste metabolites are converted by microbial breakdown in the recirculating system filters—where ammonia is converted to nitrate by nitrifying bacteria (Love et al., 2014); and nutrients are absorbed by the plants cultivated hydroponically (Rakocy et al., 2011). Solid fish waste eliminated after food digestion provides most of the nutrients required for plant nutrition, except calcium and iron, which are commonly supplemented. The aquaculture effluent flows through deep-flow culture hydroponic troughs, and a closed system recirculates the water back to the fish-rearing tanks for reuse (Rakocy et al., 2011).
The integration of fish and vegetable production in the UVI Commercial Aquaponics System uses a small land area, conserves water, limits waste discharged into the environment (Boxman et al., 2017), and recovers nutrients from fish production into valuable vegetable crops. A standard protocol has been developed for the production of Nile tilapia (Oreochromis niloticus), which yields up to 11,000 lb per annum (Rakocy et al., 2006). The production of many vegetable crops also has been studied, but because of specific growth patterns and differences of marketable product, no single protocol is promoted.
In general, leafy vegetables grow well with the abundant nitrogen in the system, have a short production period, and are in high demand. Lettuce (Lactuca sativa) has been produced continuously in the UVI Commercial Aquaponics System, including a diversity of cultivars and cultural practices (Rakocy et al., 1997). Economic studies of lettuce and basil production also have been conducted (Bailey et al., 1997; Rakocy et al., 2004a). Each crop yields different revenue per unit area, and this variation must be considered when selecting cultivars to produce and obtain the highest returns for the farmer (Bailey and Ferrarezi, 2017).
Basil is a fast-growing crop commonly cultivated in aquaponics systems by commercial producers, hobbyists, and educators (Love et al., 2014). The crop’s distinctive aroma and flavor derive from essential oils, plant phenolics, flavonoids, and phenylpropanoids (Juliani and Simon, 2002). The genus Ocimum comprises more than 30 species, and is divided into basil types, which include sweet (Ocimum basilicum), lemon (Ocimum citriodorum), dwarf bush (Ocimum minimum), purple (O. basilicum var. purpurescens), and thai (O. basilicum var. thyrsiflorum). Basil cultivars can be produced for different target markets such as essential oils, pharmaceuticals, ornamental plants, or as a culinary herb for fresh or dry spices (Kaurinovic et al., 2011; Walters and Currey, 2015). Purple basils contain higher anthocyanin levels (Simon et al., 1999) and are grown for culinary purposes and teas, especially as a potential source of anthocyanins because of antioxidant properties (Juliani and Simon, 2002). Basil can be produced in aquaponics using one planting date (batch) or staggered planting dates, resulting in the production of 7.8 and 7.2 kg·m−2 of shoot fresh weight, respectively, with a density of 8 plants/m2 (Rakocy et al., 2004b).
Choosing high-value crops is one of the strategies to maximize income in aquaponics systems (Dediu et al., 2012), increasing grower portfolio and minimizing the production risks. Previous research has indicated that basil is a high-value crop for aquaponics (Rakocy et al., 2004b). However, little research has been conducted to produce different basil types and cultivars in commercial-scale aquaponics (Love et al., 2015). Walters and Currey (2015) recently compared hydroponics systems and basil cultivars in greenhouse conditions with environmental control. Saha et al. (2016) cultivated basil under soilless agricultural systems (aquaponics vs. hydroponics), without indicating how different cultivars perform. The evaluation of plant adaptation in tropical conditions is essential to recommend new cultivars for the UVI Commercial Aquaponics System. Yield per area is a primary concern so that cultivars with the greatest biomass can be selected to maximize the production per area. Plant height, width, leaf area, number of leaves, and other aspects of plant morphology are also useful to evaluate crop performance. Our objective was to identify suitable basil cultivars for tropical outdoor aquaponics production using the UVI Commercial Aquaponics System to support farmers picking adapted cultivars.
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