Basil (Ocimum basilicum) Cultivation in Decoupled Aquaponics with Three Hydro-Components (Grow Pipes, Raft, Gravel) and African Catfish (Clarias gariepinus) Production in Northern Germany

Abstract

Basil (Ocimum basilicum) was cultivated in northern Germany in three different hydroponic components: grow pipes, a raft, and an ebb-and-flood gravel substrate. The nutrients originated from the intensive production of African catfish (Clarias gariepinus) with 140 fish/m3 under decoupled aquaponic conditions. After 41 days, plants were significantly taller in the gravel components (101.8 ± 8.3 cm), followed by the grow pipes (96.7 ± 7.0 cm), and the raft (94.8 ± 8.6 cm) components (gravel > grow pipes = raft). The leaf number was high and not significantly different between the grow pipes (518.0 ± 81.4), gravel (515.1 ± 133.0), and raft components (493.7 ± 124.8; grow pipes = raft = gravel). Basil in the grow-pipe subsystems developed rapid root growth and clogged the pipes with heterogeneous plant growth. Basil production in northern Germany in grow-pipe, raft, and gravel hydro-components is possible by using effluents from intensive C. gariepinus aquaculture without additional fertilizer in the plant grow-out phase. Further research should focus on optimizing grow pipes by maintaining an optimal root–water contact area, as well as on new technologies such as aquaponics (s.l.) gardening.

Growth of Basil (Ocimum basilicum) in DRF, Raft, and Grow Pipes with Effluents of African Catfish (Clarias gariepinus) in Decoupled Aquaponics

“…At 0.58%, 0.30%, and 0.16%/day (small, medium, and large fish), the results showed the expected values based on the limited feeding rate. At 80% feeding, SGR values of 3.23%, 1.50%, and 0.90%/day can be expected [14]. The small-and medium-sized fish had, on average, five times and the large fish three times the daily growth rate, with 80% and 25% feeding, respectively.…”

“…A similar study achieved FCR values of 0.97, 1.23, and 2.69, where also 25% of the recommended amount of a commercial feed was fed, and thus a large part of the feed energy was used for basal metabolism and not for growth [40]. High feed conversion ratios of the African catfish, such as FCR 0.74, 0.84, and 0.91 [14], and 0.72, 0.87, and 0.97 [41], have been reached at 80% of the maximum recommended feed amount. However, the 25% feeding was sufficient in this experiment to produce stable water conditions for the aquaponics plant production and an EC (Electric Conductivity) value of over 2000 μS/cm.…”

“…Optimum EC levels for basil cultivation in hydroponics under use of mineral fertilizer also differs, ranging from 1000 to 1600 μS/cm [47], and 2800 to 3100 μS/cm [48]. With the same experimental design and a lower mean EC level (1619.4 ± 205.6 μS/cm), basil shoot axis height (plant height above ground after 35 days) was higher and leaf numbers were substantially greater in growth pipes, raft, and gravel substrate ebb-and-flood hydro-components [14].…”

“…The demand for basil is very high among aquaponics and hydroponics producer groups [11]. As basil is particularly suitable for soilless cultivation, it has therefore been used in various aquaponics and hydroponics experiments [12][13][14]. Basil can produce 1.8 kg per m 2 under aquaponic production [15], whereas basil in soil cultivation can produce only 0.6 kg per m 2 [15].…”

“…In combination with C. gariepinus and Nile tilapia (Oreochromis niloticus), basil (O. basilicum) showed good growth performance in an extensive coupled ebb and flood gravel substrate system [16]. However, few studies report on basil under decoupled aquaponics in different hydroponic subsystems or components [14].…”