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Manipulating ph
There are simple methods to manipulate the pH in aquaponic units. In regions with limestone or chalk bedrock, the natural water is often hard with high pH. Therefore, periodic acid additions may be necessary to lower the pH. In regions with volcanic bedrock, the natural water will often be soft, with very low alkalinity, indicating a need to periodically add a base or a carbonate buffer to the water to counteract the natural acidification of the aquaponic unit.
· Food and Agriculture Organization of the United NationsManagement practices for plants
Seedlings can be planted into the system as soon as nitrates are detected. Expect these first plants to grow slowly and exhibit some temporary deficiencies because the nutrient supply in the water is temporarily small. It is recommended to wait 3-4 weeks to allow the nutrients to accrue. In general, aquaponic systems show a slightly lower growth rate than soil or hydroponic production in the first six weeks. However, once a sufficient nutrient base has been built within the unit (1-3 months) the plant growth rates become 2-3 times faster than in soil.
· Food and Agriculture Organization of the United NationsManagement practices for fish
Adding fish to a new aquaponic unit is an important event. It is best to wait until the initial cycling process is totally completed and the biofilter is fully functioning. Ideally, the ammonia and nitrite are at zero and nitrates are beginning to rise. This is the safest time to add fish. If it is decided to add fish before cycling, then a reduced number of fish should be added. This time will be very stressful for the fish, and water changes may be necessary.
· Food and Agriculture Organization of the United NationsMajor differences between soil and soil-less crop production
There are many similarities between in-ground soil-based agriculture and soil- less production, while the basic plant biology is always the same (Figures 6.1 and 6.2). However it is worth investigating major differences between soil and soil-less production (Table 6.1) in order to bridge the gap between traditional in-ground practices and newer soil-less techniques. Generally, the differences are between the use of fertilizer and consumption of water, the ability to use non-arable land, and overall productivity.
· Food and Agriculture Organization of the United NationsMaintaining a healthy bacterial colony
The major parameters affecting bacteria growth that should be considered when maintaining a healthy biofilter are adequate surface area and appropriate water conditions. Surface area Bacterial colonies will thrive on any material, such as plant roots, along fish tank walls and inside each grow pipe. The total available area available for these bacteria will determine how much ammonia they are able to metabolize. Depending on the fish biomass and system design, the plant roots and tank walls can provide adequate area.
· Food and Agriculture Organization of the United NationsIntegrating aquaponics with other gardens
Aquaponics can be used alone, but it becomes a stronger tool for the small-scale farmer when used in conjunction with other agriculture techniques. It has already been discussed how other plants and insects can be grown to supplement the fishes’ diet, but aquaponics can also help the rest of the garden. Generally, the nutrient-rich water from the aquaponic units can be shared among other plant production areas. Irrigation and fertilization Aquaponic units are a source of nutrient-rich water for vegetable production.
· Food and Agriculture Organization of the United NationsImportant biological components of aquaponics
As described in Chapter 1, aquaponics is a form of integrated agriculture that combines two major techniques, aquaculture and hydroponics. In one continuously recirculating unit, culture water exits the fish tank containing the metabolic wastes of fish. The water first passes through a mechanical filter that captures solid wastes, and then passes through a biofilter that oxidizes ammonia to nitrate. The water then travels through plant grow beds where plants uptake the nutrients, and finally the water returns, purified, to the fish tank (Figure 2.
· Food and Agriculture Organization of the United NationsHydroponics and soil-less culture
Soil-less culture is the method of growing agricultural crops without the use of soil. Instead of soil, various inert growing media, also called substrates, are used. These media provide plant support and moisture retention. Irrigation systems are integrated within these media, thereby introducing a nutrient solution to the plants’ root zones. This solution provides all of the necessary nutrients for plant growth. The most common method of soil-less culture is hydroponics, which includes growing plants either on a substrate or in an aqueous medium with bare roots.
· Food and Agriculture Organization of the United NationsHeterotrophic bacteria and mineralization
There is another important bacteria group, as well as other micro-organisms, involved in aquaponics. This bacteria group is generally called the heterotrophic group. These bacteria utilize organic carbon as its food source, and are mainly involved in the decomposition of solid fish and plant waste. Most fish only retain 30-40 percent of the food they eat, meaning that 60-70 percent of what they eat is released as waste. Of this waste, 50-70 percent is dissolved waste released as ammonia.
· Food and Agriculture Organization of the United NationsFish selection
Several fish species have recorded excellent growth rates in aquaponic units. Fish species suitable for aquaponic farming include: tilapia, common carp, silver carp, grass carp, barramundi, jade perch, catfish, trout, salmon, Murray cod, and largemouth bass. Some of these species, which are available worldwide, grow particularly well in aquaponic units and are discussed in more detail in the following sections. In planning an aquaponic facility it is critical to appreciate the importance of the availability of healthy fish from reputable local suppliers.
· Food and Agriculture Organization of the United Nations