Agri Kultuur March/ Maart 2016 - Page 24

De Cheiro Da Norte Chilli ratio of 1 m3 of fish rearing tank to 2 m3 of pea gravel 3 to 6 cm in diameter as hydroponic media is recommended for reciprocating (flood and drain) gravel aquaponic systems. This ratio requires that tilapia are raised to a final stocking density of 60 kg/m3 and fed appropriately. With the recommended ratio no solids are removed from the system. The hydroponic beds should be cultivated (stirred up) between crops and inoculated with red worms to help break down and assimilate the organic matter. With this system nutrient supplementation may not be necessarily. As a general guide for raft aquaponics, a ratio in the range of 60100 g of fish feed/m2 of plant growing area per day should be used. Ratios within this range have been used successfully in the UVI system for the production of tilapia, lettuce, basil and several other plants. In the UVI system all solids are removed, with a residence time of ˂1 day for settleable solids (>100 microns) removed by a clarifier, and 3 to 7 days for suspended solids removed by an orchard netting filter. The system uses rainwater, and sup- Candy Plum Tomato plementation is required for potassium, calcium, and iron. Pest and Disease Control: Aquaponic systems are characterized by a broader range of microflora and -fauna than conventional hydroponic systems, especially because the cultivation of fish and biofiltration occurs in the same water loop. Conventional pesticides that are used in hydroponics cannot be used in aquaponics because of toxicity risk to the fish and to the desired biofilm (e.g., autotrophic nitrifying biofilm). The need to maintain the nitrification biofilm and other nutrient solubilizing microorganisms also prevents the use of antibiotics and fungicides for fish pathogen control and removal in the aquatic environment. Furthermore, antibiotics are not allowed for plant application so their use against fish pathogens must be avoided in aquaponic systems. These constraints demand innovative pest and disease management solutions for fish and plants that minimize impacts on fish and desired microorganisms. Plant and fish pests and pathogens can be divided into four different catego- Malaga ries based on specific alternative treatment solutions. These are (1) plant pests – mostly insects that damage the leaves and roots (e.g., aphids, spider mites); (2) plant diseases – microorganisms (e.g., bacteria, fungi) and viruses that attack plants; (3) fish parasites (e.g., monogenean, cestoda); and (4) fish diseases caused by viruses and microorganisms. Rearing and crop practices that decrease the occurrence of diseases could be applied such as preventative sanitary measures, low density of fish and/or plants, and/or control of environmental conditions, which decrease relative humidity around the plants. In addition to these practices, a few innovative methods of biological control already exist for plants cultivated under field or greenhouse conditions. These methods are based on the use of microorganisms with biocontrol activity, or extracts of such microorganisms or extracts of plants (including essential oils) that show high antimicrobial efficiency and short residence time. Vegetable Selection: Many types of vegetables have