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This chapter discusses the theory and practice needed for successful plant production in aquaponic systems. First, it highlights some of the major differences between ground-grown crop production and soil-less crop production. Following this, there is a discussion on some essential plant biology and plant nutrition concepts, focusing on the most important aspects for aquaponics. After, there is a brief section on recommendations for selecting vegetables to grow in aquaponic units. The final two sections cover plant health, methods to maintain plant health, and some advice on how to make the most of the plant growing space.
In many commercial aquaponic ventures, the vegetable production is more profitable than the fish. However, there are exceptions, and some farmers earn more from particularly valuable fish. Estimates from commercial aquaponic units predominantly in the West suggest that up to 90 percent of the financial gains can come from plant production. One reason is the fast turnover rate of vegetables compared with the fish. Further information on aquaponic plant production is covered in Chapter 8 and in the appendixes. Chapter 8 discusses practices to manage plant production through the seasons, and discusses different approaches for each of the hydroponic methods (media bed, NFT and DWC). Appendix 1 is a technical description of 12 popular vegetables to grow in aquaponics; Appendix 2 contains descriptions and tables detailing several organic treatments of pests and diseases.
The major advantages of aquaponics over soil agriculture are: (i) no wasted fertilizer; (ii) lower water use; (iii) higher productivity/quality; (iv) ability to utilize non-arable land; and (v) offset of tillage, weeding and other traditional agricultural tasks.
Plants require sunlight, air, water and nutrients to grow. Essential macronutrients include: nitrogen, phosphorus, potassium, calcium, magnesium and sulphur; Micronutrients include iron, zinc, boron, copper, manganese and molybdenum. Deficiencies need to be addressed by supplying the limiting nutrients with supplemental fertilizer or increasing mineralization.
The most important water quality parameter for plants is pH because it affects the availability of essential nutrients.
The suitable temperature range for most vegetables is 18-26 °C, although many vegetables are seasonal. Winter vegetables require temperatures of 8-20 °C, and summer vegetables require temperatures of 17-30 °C.
Leafy green herbs and vegetables do extremely well in aquaponics. Large fruiting vegetables are also applicable, including tomatoes, peppers, eggplant, and cucumbers, peas and beans. Root crops and tubers are less commonly grown and require special attention.
Integrated production and pest/disease management uses physical, mechanical and cultural practices to minimize pests/pathogens, and then uses fish-safe chemical and biological treatment in targeted applications, when necessary.
Intelligent planting design can maximize space, encourage beneficial insects and improve production.
Staggered planting provides continual harvest as well as a constant nutrient uptake and more consistent water quality.
Source: Food and Agriculture Organization of the United Nations, 2014, Christopher Somerville, Moti Cohen, Edoardo Pantanella, Austin Stankus and Alessandro Lovatelli, Small-scale aquaponic food production, http://www.fao.org/3/a-i4021e.pdf. Reproduced with permission.