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Site selection is an important aspect that must be considered before installing an aquaponic unit. This section generally refers to aquaponic units built outdoors without a greenhouse. However, there are brief comments about greenhouses and shading net structures for larger units. It is important to remember that some of the system's components, especially the water and stone media, are heavy and hard to move, so it is worth building the system in its final location. Selected sites should be on a surface that is stable and level, in an area that is protected from severe weather but exposed to substantial sunlight.
Be sure to choose a site that is stable and level. Some of the major components of an aquaponic system are heavy, leading to the potential risk of the legs of the system sinking into the ground. This can lead to disrupted water flow, flooding or catastrophic collapse. Find the most level and solid ground available. Concrete slabs are suitable, but do not allow any components to be buried, which can lead to tripping hazards. If the system is built on soil, it is useful to grade the soil and put down material to mitigate weeds. In addition, place concrete or cement blocks under the legs of the grow beds to improve stability. Stone chips are often used to level and stabilize soil locations. Moreover, it is important to place the fish tanks on a base; this will help to provide stability, protect the tank, allow for plumbing and drains on the tank bottom, and thermally isolate it from the ground.
Extreme environmental conditions can stress plants and destroy structures (Figure 4.14). Strong prevailing winds can have a considerable negative impact on plant production and can cause damage to stems and reproductive parts. In addition, strong rain can harm the plants and damage unprotected electrical sockets. Large amounts of rain can dilute the nutrient-rich water, and can flood a system if no overflow mechanism is integrated into the unit. Snow causes the same problems as heavy rain, with the added threat of cold damage. It is recommended that the system be located in a wind-protected zone. If heavy rains are common, it may be worth protecting the system with a plastic-lined hoop house, although this may not be necessary in all locations.
Sunlight is critical for plants, and as such, the plants need to receive the optimum amount of sunlight during the day. Most of the common plants for aquaponics grow well in full sun conditions; however, if the sunlight is too intense, a simple shade structure can be installed over the grow beds. Some light- sensitive plants, including lettuce, salad greens and some cabbages, will bolt in too much sun, go to seed and become bitter and unpalatable. Other tropical plants adapted to the jungle floor such as turmeric and certain ornamentals can exhibit leaf burn when exposed to excessive sun, and they do better with some shade. On the other hand, with insufficient sunlight, some plants can have slow growth rates. This situation can be avoided by placing the aquaponic unit in a sunny location. If a shady area is the only location available, it is recommended that shade-tolerant species be planted.
Systems should be designed to take advantage of the sun travelling from east to west through the sky. Generally, the grow beds should be spatially arranged such that the longest side is on a north-south axis. This makes the most efficient use of the sun during the day. Alternatively, if less light is preferable, orient the beds, pipes and canals following the east-west axis. Also consider where and when there are shadows that cross the chosen site. Be careful in the arrangement of plants such that they do not inadvertently shade one another. However, it is possible to use tall, sun-loving plants to shade low, light-sensitive plants from intense afternoon sun by placing the tall plants to the west or by alternating the two in a scattered distribution.
Unlike the plants, the fish do not need direct sunlight. In fact, it is important for the fish tanks to be in the shade. Normally, the fish tanks are covered with a removable shading material that is placed on top of the tank (Figure 4.15). However, where possible, it is better to isolate the fish tanks using a separate shading structure. This will prevent algae growth (see Chapter 3) and will help to maintain a stable water temperature during the day. It is also worth preventing leaves and organic debris from entering the fish tanks, as the decaying leaf matter can stain the water, affect water chemistry and clog pipes. Either locate the system away from overhanging vegetation or keep the tank covered with a screen. Moreover, fish tanks are vulnerable to predators. Using shade netting, tarps or other screening over the fish tanks will prevent all of these threats.
In site selection, it is important to consider the availability of utilities. Electric outlets are needed for water and air pumps. These outlets should be shielded from water and equipped with a residual-current device (RCD) to reduce the risk of electrical shock; RCD adaptors can be purchased from standard hardware stores. Moreover, the water source should be easily accessible, whether it is municipal water or rain collection units. Similarly, consider where any effluent from the system would go. Although extremely water efficient, aquaponic systems occasionally require water changes, and filters and clarifiers need to be rinsed. It is convenient to have some soil plants located nearby that would benefit from this water. The system should be located where it is easy for daily access because frequent monitoring and daily feeding are required. Finally, consider if it is necessary to fence the entire section. Fences are sometimes required to prevent theft and vandalism, animal pests and for some food safety regulations.
Flat rooftops are often suitable sites for aquaponics because they are level, stable, exposed to sunlight and are not already used for agriculture (Figures 4.16-4.18). However, when building a system on a rooftop it is crucial to consider the weight of the system, and whether or not the roof is capable of supporting it. It is essential to consult with an architect or civil engineer before building a rooftop system. In addition, be sure that materials can be transported both safely and effectively to the rooftop site.
Greenhouses are not essential for small-scale aquaponic units, yet they may be useful in extending the growing season in some regions (Figures 4.19 and 4.20). This is particularly true in temperate and other cooler regions around the world, as greenhouses can be used to maintain a warm water temperature during the cold months, thereby allowing year-round production.
A greenhouse is a metal, wood or plastic frame structure that is covered by transparent nylon, plastic or glass. The purpose of this structure is to allow sunlight (solar radiation) to enter the greenhouse and then trap it so it begins heating the air inside the greenhouse. As the sun begins to set, the heat is retained in the greenhouse by the roof and walls, allowing for a warmer and more stable air temperature during a 24-hour period. Greenhouses provide general environmental protection from wind, snow and heavy rain. Greenhouses extend the growing season by retaining ambient solar heat, but can also be heated from within. Greenhouses can keep away animals and other pests, and serve as some security against theft. Greenhouses are comfortable to work in during colder seasons, and provide the grower with protection from the weather. Greenhouse frames can be used to support climbing plants or to hang shade material. Together, these advantages of a greenhouse result in higher productivity and in an extended cropping season.
However, these benefits need to be balanced against the drawbacks of greenhouses. The initial capital costs for a greenhouse can be high depending on the degree of technology and sophistication desired. Greenhouses also require additional operating costs because fans are needed to create air circulation to prevent overheating and overly humid conditions. Some diseases and insect pests are more common in greenhouses and need to be managed accordingly (i.e. use of insect nets on doors and windows), although the confined environment can favour the use of certain pest controls.
In some tropical regions, net houses are more appropriate than conventional greenhouses covered with polyethylene plastic or glass (Figure 4.21). This is because the hot climates in the tropics or subtropics raise the need for better ventilation to avoid high temperatures and humidity. Net houses consist of a frame over the grow beds that is covered with mesh netting along the four walls and a plastic roof over the top. The plastic roof is particularly important to prevent rain from entering, especially in areas with intense rainy seasons, as units could overflow in a matter of days. Net houses are used to remove the threat of many noxious pests associated with the tropics, as well as birds and larger animals. The ideal mesh size for the four walls depends on the local pests. For large insects, the mesh size should be 0.5 mm. For smaller ones, which are often vectors of viral diseases, the mesh size should be thicker (i.e. mesh 50). Net houses can provide some shade if the sunlight is too intense. Common shade materials vary from 25 to 60 percent sunblock.
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.