Nutrition and quality of aquaponic systems
Author(s)
Pantanella, Edoardo
Date Issued
May 24, 2012
Type
Doctoral Thesis
Abstract
The future of the agriculture is in the development of sustainable production systems that make
better use of inputs and by-products as well as improve quality standards under competitive costs.
Integration is seen one of the key aspects to optimize improve sustainability. In the case of
agriculture sustainability can be achieved by closing the loop between crop and animal
productions. The combination of plants with fish thus appears an optimal strategy to enhance
productivity and to reduce footprint to minimal terms. Aquaponics is a vegetable production
technique that integrates soilless cultivation with closed recirculating aquaculture systems. In
aquaponics plants grow on aquaculture wastes and reclaim water back to fish through
phytodepuration. The zero-discharge and fertilizer-free management makes aquaponics an
environmental-friendly and profitable production system. Aquaponics infact overtakes all the
pollution and input management issues that agriculture and aquaculture would have if taken
alone. Nutrient concentrations in aquaponics are sensitively lower than those used in hydroponic
systems due to the storage of nutrients into the recirculating water and the continuous supply of
minerals by fish. Although aquaponic systems have been studied for decades, vegetable quality
and productivity of aquaponics against hydroponics still needs to be fully developed. The
expansion of aquaponics to large scale commercial systems is possible providing that production
maintain same standards and quality of marketed products.
The research, carried out at the Experimental Farm of the University of Tuscia assessed the
production and quality of aquaponic productions. Several vegetables and fish species were tested
across three years of experiments to determine system efficiency and identify best farming
practices.
In the case of lettuce (Lactuca sativa L cv Integral) cropped with tilapia (Oreochromis niloticus
L.) similar productions were obtained between aquaponics and hydroponics despite the very low
levels of nitrogen (from 15 mg L-1) and electrical conductivity (0.6 dS m-1). Quality assessment
showed that chlorophyll in plants is similar if not higher to hydroponics and production does not
have harmful levels of nitrates in leaves.
The quality of basil and the influence of fish diet on water nutrients was studied in two
consecutive summer trials. For sweet basil (Ocimum basilicum L. cv superbo) African catfish
(Clarias gariepinus B.) was stocked under same densities but different protein diets (31 and 40%
protein). Productivity in aquaponics was not different from hydroponics and comparable to
literature data. The qualitative traits of plants in terms of chlorophyll and leaf/stem ratio were not
different among treatments. Nevertheless plants obtained higher leaf biomass par rapport to
literature data. Fish performance was similar to traditional recirculating systems, which suggested
2
that aquaponics is not a limiting environment for fish. Neventheless nitrogen levels grew with
double pace with higher proteins in diet. System assessment suggested that optimal nutrient
uptake efficiency occurrs when water nutrient concentrations are low.
Production and quality of fruity plants was tested in aquaponics with the aim to assess system
performance under lower potassium concentrations than hydroponics. Cucumber (Cucumis
sativus L. cv Ekron) grew on largemouth bass (Micropterus salmoides L.) wastewater in a
summer crop under greenhouse environment. Yields, marketable product (fruit weight above 180
g), pH, brix degree and tritatable acidity were similar to hydroponics. Likewise nitrogen uptake
efficiency appeared similar despite higher nitrogen losses in aquaponics due to ecosystem's
metabolism.
Aquaponics could also integrate marine farming through salt-tolerant species. Impact of marine
aquaculture can be attenuated by using plants that are widely used in horticulture as specialty
salads. Three Salsola soda trials were carried out with mullet (Mugil cephalus L) under raising
salt concentrations: 5 g L-1, 10 g L-1, 20 g L-1, 30 g L-1. Production and nutrient uptake were
assessed to determine the stripping capacity and the salt accumulation of the plants. Salinity at 10
g L-1 resulted the most productive, but interesting growth was observed till 20 g L-1 of salt.
Aquaponics proved to be more performing than hydroponics even though nitrogen levels were 3-5
times lower thus confirming the good potential of cropping high value vegetables as a
phytoremediation strategy.
The choice of growing method is a critical factor in aquaponics. Not only is growth affected by
nutrient concentrations, but also by delivery systems. Growth performance in lettuce (Lactuca
sativa L. cv Verde degli Ortolani) was assessed on floating system, NFT and substrate system for
three consecutive crops under growing nutrient concentrations. Results showed high productions
from floating systems, which was the most constant system in terms of output. However NFT
resulted outperforming (+18%) whenever proper nutrient concentrations, flow rate and root/water
volume was guaranteed. Substrate aquaponics resulted always underperforming by 30-40% due to
inadequate nutrient exchange at root level. Results suggested NFT as the most performing method
to strip nutrients from water, providing that optimal nutrient flow is guaranteed at root level.
Research assessed food safety aspects and the compliance to national or international regulations
on microbial loads for irrigation water. Although products appear safe due to the water delivery
methods used (subirrigation instead of aspersion) presence of bacteria in water above set levels
may be a limiting factor that may exclude aquaponics from HAACP driven productions. An
assessment of UV-treated aquaponics against untreated systems showed more than 99% total
coliform abatement and the compliance to EU regulations for irrigation water. Moreover
productivity of both lettuce (Lactuca sativa L. cv Verde degli Ortolani) and tilapia (Oreochromis
niloticus L.) was not affected by sterilization.
Additional information
Dottorato di ricerca in Ortoflorofrutticoltura
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