Choosing Your Growing Systems

Transcription

1 Choosing Your Growing Systems Aquaponics is the integration of recirculating aquaculture and hydroponics...in all of its forms. In this section, we consider the range of hydroponic growing systems that are available for use with aquaponics systems. Overview The choice of growing system will be largely driven by your resources and personal preferences. Other factors that will impact the choice of a growing system include: the type of plants to be grown how hands on you want to be the cultural needs of the plants The thing to remember is that no single growing system is ideally suited to all plants, so you ll probably end up with more than one type of system.and you do have a wide range of choices. Aquaponics is the integration of recirculating aquaculture and hydroponic growing systems so (theoretically) any hydroponic system can be used for aquaponics. In practice, however, some hydro systems are better suited to urban aquaponics than others. For the purposes of aquaponics, hydroponic systems include the following: Media- based Grow Beds where various types of media are used to support the plants. Nutrient Flow Systems - where the plants are given direct access to the nutrient flow. Examples include nutrient film technique (NFT), deep water culture (DWC) and raft. Other options generally include smaller systems like satellite pots, the Tray system and Autopot. Media- based Grow Beds Grow beds are the most popular growing system in use by backyard aquaponicists. They usually comprise a large waterproof tray that contains media which supports the plants. They may be made of fibreglass, plastic, corrugated steel and wood or plywood (fitted with a suitable liner). Old bathtubs and plastic barrels are also frequently recycled for use as grow beds. Probably the person most responsible for the current interest in gravel grow beds was Missouri farmer (and aquaponics pioneer) Tom Speraneo. While he wasn t the first to use media- based grow beds (hydroponicists had been using them for decades) and he wasn t even the first to use them in aquaponics (UVI had tried and rejected them years earlier), he made them work for his purposes and he popularised their use.

2 2 Virtually any media used in hydroponics can be adapted for use in aquaponics. Your circumstances and preferences will drive your choice of media. Here are the main options: Gravel is cheap to purchase - anchors plant roots very well is very heavy - is as hard on the hands as it is on the back - washing gravel will consume large amounts of water. Some gravel is not inert and may contribute to ph spikes or mineral imbalances. Light Expanded Clay Aggregate much lighter than gravel but much more expensive better than gravel to work with. Vermiculite great water retention works best with open loop (non- recirculating) systems where timers control the watering cycle. Coco Coir good water retention will discolour the fish tank water so best used with open loop systems some brands may be calcium- deficient and/or may contain high levels of sodium rinse before use. Spent coco coir can be recycled through other backyard food production systems such as poultry litter and worm bedding. Perlite very light - will gradually break up and has the unhappy knack of jamming pumps best used in open loop situations - probably my least favourite aquaponics media. Continuous flow or Flood and Drain? If you decide to use media- based grow beds, you have three options when it comes to the watering method: flood and drain continuous flow #1 (surface) continuous flow #2 (sub- surface) Each method has its own advantages and some limitations. Flood and Drain This watering regime is also known in hydroponic circles as ebb and flow. With the flood and drain method, the movement of water is controlled by timers, float switches or auto- syphons. As the name suggests, flood and drain grow beds fill up and then empty - in a continuous cycle. The benefits of this system include excellent aeration and nitrification.and the plants have unrestricted access to water and nutrients. The issues with the flood and drain method include: fluctuating water level in the fish tank requirement for a larger sump tank ongoing need for adjustments to timers, float switches or auto- syphons. Continuous Flow #1 (surface) This method features a PVC watering grid which consists of pipes with holes drilled at pre-

3 3 determined intervals. Seedlings are planted adjacent to each hole so that they receive a constant flow of nutrient- rich water. Aeration is excellent and (depending on the design of the watering grid) nitrification can be quite good, too. The disadvantages of this method are that the water is exposed to sunlight as it flows from the watering grid (and that may create the conditions for algal blooms) and plenty of flow is required to ensure that adequate water issues from the holes in the grid. Continuous Flow #2 (sub- surface) With this option, the nutrient- rich water enters one end of the grow bed and exits at the other end. The water is maintained at a predetermined depth. Expanded clay pebbles are the preferred media for this option because of their capacity for hydration the water wicks upwards to create a damp (but not wet) zone at the base of the plants. Eventually, the plant roots grow down into the water while the plant crown remains dry. This ensures that the plant gets all of the water and nutrients that it needs without becoming waterlogged. Sub- surface continuous watering has a number of benefits including: simplicity and reliability there are no control devices to malfunction or get out of adjustment constant availability of water and nutrients lower build cost no need for timers, float switches or auto- syphons smaller pumps can be used lower energy consumption water re- entering the fish tank contains fewer solids the lower water velocity allows any solids to settle out and to be trapped by the media more effectively reduced algae problems because the inflow to the grow bed is beneath the clay pebble media Prospective issues with sub- surface watering systems include: lower nitrification rates less aeration I resolve both issues by inserting a trickle bio- filter into the water column immediately before the fish tank. Not only does this ensure optimum nitrification and aeration, the solids loading is limited to dissolved solids. My Preference While I have plenty of experience with flood and drain systems (and I love watching auto- syphons kick in and out), I prefer sub- surface continuous flow watering for media- based grow beds. I design aquaponics systems for maximum productivity which requires capture and removal of solid wastes, environmental control and a strategic approach to grow bed management.

4 4 My latest design, The Queenslander, features sedimentation and mineralisation devices - and a Moving Bed bio- filter, which optimises water quality. The design also includes at least one continuous flow (sub- surface) grow bed. The way the grow bed is set up and managed also influences water quality. I place 150mm of clay pebble media in the beds and set the water depth to about 40mm. This ensures that the clay pebbles get hydrated to the correct level for the plants. We plant this grow bed out to short cycle plants like lettuce, Asian greens and soft herbs. This allows us to harvest the entire bed before cleaning it and this happens on a five to six week cycle. The depth of the media makes for quick and easy cleaning. As the water exits the grow bed, it drains into the sump. From there, some of the water is pumped back into the fish tank. The surplus flow is directed through the bio- filter where any aeration or nitrification shortfall is resolved. In my experience, there is no discernible difference between flood and drain or continuous flow when it comes to plant growth. Grow Bed Depth Optimum grow bed depth is often the subject of hot debate among aquaponicists. There are those who argue that grow beds should not be less than 300mm in depth but the reality is that they can be less than that, so long as the plants are adequately supported and (to ensure the ongoing health of the nitrifying bacteria) the media remains moist and at a consistent temperature between watering cycles. In practice, I have found that properly managed grow beds can be as little as 100mm and will work just as well as the deeper ones. In fact, there are some benefits to be gained from using shallow grow beds. Cleaning shallow grow beds is a much easier task than it is with 300mm ones..and filling them with media is a much less expensive undertaking. A 150mm grow bed will require half of the media of a 300mm one..at half the cost and half the weight. A shallow grow bed can be made of less robust materials because it doesn t need to support the same weight. Some other thoughts on Grow Beds: They can be used in place of (or in addition to) trickling bio- filters. Blue plastic drums can be cut in half (vertically or horizontally) for use as grow beds. Cut in half on the vertical plane, a drum becomes two large tubs that can be used for dwarf fruit trees and other large plants like zucchini. If you decide to use plastic grow beds, consider the weight of the media. Only the strongest plastic containers will support the use of gravel. Elevated grow beds will (because of their weight) require robust supports. These may be made from steel, hardwood, concrete block or a combination of these materials.

5 5 Nutrient Flow Systems Most commercial aquaponics systems are nutrient flow systems..either Nutrient Film Technique (NFT) or Deep Water Culture (DWC). Nutrient Film Technique (NFT) NFT is a very useful means of growing a variety of salad crops. Plastic troughs are used to transport a shallow trickle of nutrient- rich water past the bare roots of plants. Like most other nutrient flow systems, mechanical filtration is essential in an NFT unit - to keep the plant roots free of fish solids that would otherwise restrict the uptake of oxygen and nutrients. NFT is the most popular hydroponic system in commercial use but it enjoys limited interest in small- scale aquaponics largely due to its requirement for intensive management. Having said that, we operate a small NFT set up with which we grow some very good mignonette lettuce.under quite ordinary management. The benefits of NFT systems include: Good oxygen exposure to the nutrient flow. Good access to water and nutrients. Portability..we often move our small NFT unit from one fish tank to another. The most obvious downside of NFT is that, in the event of a pump failure or pipe blockage, your plants begin to suffer very soon after the water stops flowing. The other big issue with NFT that hot weather can result in high root zone temperatures that are prejudicial to the plants. Deep Water Culture (DWC) Raft Culture The raft growing system is a variation on the DWC theme and most widely used DWC approach. The oldest commercial raft installation is that belonging to the University of Virgin Islands. This system has operated for over 25 years and, through the work of James Rakocy PhD and his associates, has provided much of the research data that surrounds aquaponics. The UVI aquaponics system has also been widely replicated throughout the world. Typically, a raft system will comprise: Fish tanks Sump tank Water pump Air blower Solids removal devices like a swirl filter, clarifier or sedimentation tank Grow tanks Styrofoam raft plant supports

6 6 Raft systems use deep troughs or grow tanks to produce plants. Where grow beds are filled with media, grow tanks contain nutrient- rich water. Rafts (often made of expanded polystyrene sheet) float on the water. Seedlings are usually placed in net pots that are inserted into holes that have been cut into the expanded polystyrene sheet. An alternative to the use of rafts is to support the plants above the water on a growing deck. The plants are contained in net pots filled with expanded clay and rest in holes cut into the growing deck. A simple adjustable weir arrangement ensures that just the plant roots are in contact with the water without immersing the stem/root crown. The water level in the tank can be adjusted as the plants grow. UVI use 1.5 Styrofoam (a Dow product) for rafts in preference to expanded polystyrene foam - because it s stronger. Rafts are often painted with a non- toxic paint to further protect them from the sun. While backyard aquaponicists have been slow to embrace raft systems, they offer significant benefits over both media- based and NFT systems including: They are simple to build and easy to operate. They provide for greater stability in root zone temperatures. They contain a much larger volume of water for a given footprint than media- based or NFT systems, which means that: Fish may be stocked at higher densities Feeding rates can be higher Such systems offer a greater margin of operating safety in the event of equipment failure. Temperature fluctuations are buffered. They are more portable..relocation of a small raft system is a simple matter of pumping out the water and moving the components. There is a substantial body of research and operating information available. Any grow bed that is suitable for flood and drain operation can be used for raft systems. Grow tanks can also be fabricated from wood, bricks, ferro- cement or poured concrete and fitted with a liner. Depending on the nature of their manufacture, they can be raised on located on the ground. If they are located on the ground, use a thick barrier (like recycled carpet) to prevent sharp stones or sticks from penetrating the liner. Nut (sedge) grass is a problem in our area and it is well capable of holing anything but the most robust of liners. The optimum width for such tanks is 1200mm (4 feet) to allow unfettered access to the plants from either side. Premised upon the UVI experience, they can be any length up to 30 metres (over 90 feet) long. Narrow grow tanks (of around 600mm) are well suited to growing tomato row crops. Rectangular plastic or fibreglass livestock troughs can be converted for backyard raft systems, too. While commercial grow tanks are usually 300mm 450mm deep, domestic tanks can be anything

7 7 over 150mm. The water recirculates through a raft system continuously and usually at a higher rate of flow than media or NFT systems. One of the things that raft systems have in common with NFT units is the need to remove as much of the solid waste from the water as possible. A clarifier or similar solids removal device will trap those solids that settle out and a mineralisation tank will assist in the removal of the suspended particulates that slip through. This will assist nitrification and plant health because (otherwise) the solids will attach to the roots of the plants and retard their growth. It will also facilitate the mineralisation of the solids so that a wider range of nutrients is available to the plants. Where media- based systems rely on the grow beds to facilitate the colonisation of bacteria, the underside of the expanded polystyrene rafts and the walls of the grow tanks perform a similar function in large raft systems. Personally, I d still incorporate a trickling biological filter into a backyard raft system just to be sure of adequate nitrification and to provide some flexibility in the event that it became necessary (for whatever reason) to separate the fish tank from the growing system. Good aeration right throughout a raft system is essential. Plenty of oxygen is good for the fish, the plants and the bacteria. Grow tanks should be fitted with air lines and diffusers to ensure that the water in the tanks is well aerated at all times. These should be cleaned at regular intervals to ensure that they are working as they should. While raft installations are most often used to grow salad greens, herbs and Asian greens, they can also accommodate larger plants like zucchini or vine crops like tomatoes or cucumbers. Raft aquaponics systems can be designed specifically for fish, plants or available space. Small- scale DWC Another approach to DWC consists of a series of buckets connected to each other and to a fish tank. The water from the fish tank is recirculated through the buckets. Each bucket has a lid that supports a net pot. Seedlings are placed into the net pot so that their roots are in contact with the water. An air stone for each bucket will ensure ample aeration and healthy plant roots. In the few instances where I have seen this system at work it has been very productive. This approach to DWC is particularly well suited to use with large plants. Other Options Satellite Pots Satellite pots are large (300mm and 440mm) plastic pots that are filled with a suitable medium into which seedlings are planted. Large holes bored in the base of these pots ensure good drainage.

8 8 The planter pots are inserted into drain pots. Several pots may be connected to each so that the water can, depending on the media, be drained back to the fish tank. An even better arrangement is to insert the drain hose into a pipe so that blockages can be cleared with less effort and the entire satellite pot can be moved as required Satellite pots offer a number of specific benefits including: Each plant has its own growing environment and has no need to compete with other plants to get its share of nutrient or water. Individual plants can be inserted or removed at will. Plants can be accommodated in irregularly shaped or narrow spaces. Disease control when a plant is diseased or infested, it can be removed from the growing area to avoid spreading the disease or infestation..or to allow for treatment of the problem without affecting the fish. Ease of management the pots or trays can be located at a good working height and are easily moved about for planting or harvesting. Versatility this system compliments the tray system by accommodating deep- rooted plants. Tray System The tray system is based on plastic containers (330mm X 660mm X 140mm) filled with vermiculite, perlite, coco coir.or any mix of these. This system was developed by Joe Romer and is described in his excellent book Hydroponic Gardening in Australia. The tray system is well suited to the growing of small crops including salad greens, herbs, dwarf beans and Asian greens like bok choi or pak choi. Having said that, I ve seen tomatoes and silver beet growing in these trays, too. This simple system offers a range of benefits including: Productivity each tray will yield several crops of lettuce or soft herbs each year. Simplicity it requires no pumps in its simplest form and it assumes virtually little skill or knowledge on the part of the operator. Ease of assembly and operation a 12mm drain hole is drilled in one end of the tray about 20mm from the bottom. Simply pour nutrient- rich water into the tray until it drips from the drain hole. Satellite pots and Tray system gardens have a number of common benefits including: Lightweight suited to balconies and decks. Versatility the growing system can be expanded a pot or a tray at a time..as you need (and can afford) them. Operator comfort the pots and trays can be located on a raised bench for ease of access. Portability you can take the garden wherever you want one pot or tray at a time - useful for potting or harvesting. An entire garden can be picked up and moved virtually anywhere - great for people who rent their homes. Suitable media for satellite pots and the tray system include clay pebbles, vermiculite, perlite or coco coir or a combination of these. Where expanded clay is used, the water can be drained directly

9 9 back into the fish tank. Where satellite pots or trays contain vermiculite, perlite or coco coir they are usually watered at timed intervals. Autopot and the Smart Valve Another variation on the aquaponics theme involves the use of the Autopot hydroponic system. Autopot is the brainchild of Mr Jim Fah, a Malaysian- born Australian engineer who lives in Melbourne. At the core of the Autopot concept is the aptly named Smart Valve. This clever device is designed to enable individual plants to obtain water at the precise rate at which they need it. This differs from automated systems that give plants a predetermined amount of nutrient at regular intervals. The Autopot system requires no electricity, pumps or electronic control systems. Basically, the Smart Valve allows a measured amount of water to flow into a tray into which plant pots are inserted. Only once the plants have consumed this water, will the valve open to allow more water into the tray. One type of plant may require large quantities of water (like a fruiting tomato plant) while others may (in the same environment) succumb to over- watering. A system that allows the plants to access nutrient- rich water, as (and in the precise amounts) that they need it, is a great idea. So, what does all of this mean in an aquaponics context? Well, Jim Fah has integrated his Smart Valve concept with a simple recirculating aquaculture system. He has 1500 plants in Autopots, which are fed by water from fish tanks. The plants use 1000 litres of water daily in winter and 2000 litres in summer. Basically, Jim is parking his fish in the water that is earmarked for the plants. The throughput of water is such that it is not in the fish tank long enough for ammonia to build up to the point where it becomes problematic. This avoids the need for grow beds, bio- filters and water tests. How then do the plants get nutrients? A small battery- operated pump and dosing unit moves the water from the fish tanks to the Autopot units. In the process, it measures and dispenses the correct amount of hydroponic nutrient. In Jim s system, the plants are the main game - the fish are a by- product. Interestingly, plants are usually the main output (if not always the main interest) of most aquaponics systems..particularly backyard ones. Which growing system is best? If you have commercial aspirations, raft culture is the most likely choice..and, in my mind, NFT would probably come second. In my view, gravel grow beds are not generally feasible for

10 10 commercial purposes. For backyard purposes, it s a toss up. Since no single system is suited to every type of plant, it s likely that you might want to try a couple at least. While I would probably opt for grow beds, raft and NFT (in that order), I urge you to experiment a little to find out what suits you best. If you've got very limited space (like a courtyard or patio), you might even want to consider Autopot, satellite pots or the Tray system. Fish Tank to Grow Bed Ratio I frequently get asked how many grow beds (or other growing system units) are required for a fish tank of a given size. The Fish Tank to Grow Bed Ratio (also known as the Component Ratio) is an attempt to match the volume of fish tank water to the volume of grow beds. Ratios of 1:1 or 1:2 are commonly recommended. In practice, the quantity of plants that any aquaponics system can support is determined by its capacity to produce the nitrates that will sustain the plants, so there are several factors that impact the Component Ratio including: Fish species Weight of fish in the tank Bio- filter capacity Feeding rates Feed protein levels Plant species The age of the system is another factor in determining the growing capacity of an aquaponics unit. It may take up to 6 months for a media- based grow bed system to settle down to optimum nitrate production and a further two years to realise its full potential. With raft systems, it s different again. Dr James Rakocy determines the balance between fish and plants through a feeding ratio based on the daily fish- feeding rate per unit of plant growing surface area. At UVI, he feeds between 60 grams (for lettuce and staggered plantings) and 100 grams (for fruiting plants and batch plantings) of feed per square metre of plant growing space per day. Your system can be designed to favour the production of either fish or vegetables..or to suit available space and this will also be reflected in the component ratio. - o0o-