Variations on the Aquaponics Theme

Transcription

1 Variations on the Aquaponics Theme The basic recirculating aquaponics system is unquestionably a useful means by which to produce fish and plants. It is, however, not the only way that the production of fish and plants can be integrated and, in some circumstances, it may not even be the best way. In this section, we look at some other growing system options. Fish Tank Water and Soil- Based Gardening Are you a little bit excited by the thought of raising your own fish.but less so at the thought of having to use hydroponic systems to grow your vegetables and herbs? Do you struggle with the idea of having to buy/build a network of grow beds? Are you reluctant to abandon a tried and tested soil- based gardening system that has worked well for you? Maybe you re keen to try aquaponics but you want to keep your soil- based garden, too. Have you considered integrating an aquaponics system into your soil- based gardening regime? As good as they are, the hydroponic growing systems that are most often used in aquaponics are not suited to every type of plant. Growing root crops, potatoes, sweetcorn and many large plants (like zucchini, squash, pumpkins and melons) usually favour other non- hydroponic gardening options. The cost of media- based grow beds may also be an issue for some people. Consider this! Given that you have to water your plants regardless of the type of garden that you choose, why not water them with water that the fish have used first. The immediate benefit is that the water that comes from your fish tank is already loaded up with nitrates (plant food). Plants will prefer it to fresh mains water because it doesn t have chlorine in it. You are effectively producing a crop of fish for the same amount of water that you would have needed for your plants anyway and, depending on your choice of growing system, you may still be able to largely avoid the need for purchased chemical fertilisers. The principal benefit of recirculating aquaponics is arguably its efficient use of water. People are attracted to the idea that the only water that is used in many aquaponics systems is that consumed by the plants or the small amount lost to evaporation. The Case for Water Replacement The truth is that water replacement is actually good for an aquaponics system.

2 2 Over time, nitrate and phosphate levels may exceed the needs of the plants. While not toxic in the same way as ammonia or nitrite, nitrate can be converted back to nitrite in certain circumstances and they may also contribute to off flavours (the muddy taste that some people complain about in freshwater fish). Dead bacteria accumulate in an aquaponics system. While some proprietary fish pellets discolour the water in an aquaponics system, the other explanation for tea- coloured water is the presence of dead bacteria. The biofilm that form on all of the surfaces that are exposed to water in an aquaponics system are the accumulation of bacteria - dead and alive. The bottom line with dead bacteria is that they do nothing useful in an AP system and they do contribute to clogging pipework - so minimising their numbers is a useful thing to do. The main case for water replacement has to do with solids. Many particulates are too small to be removed by conventional particulate filters but still produce ammonia, consume oxygen and may irritate the fish' gills. Periodic water exchange will, in conjunction with other mechanical and biological filtration processes, contain solids levels within acceptable limits. In any case, the real issue (in terms of water efficiency) is not that you replace water but rather what you do with the water that you change out. If you use the water that you change out for soil- based plant production (particularly if the growing system is water- wise) then there is absolutely no waste issue. Indeed, if you use the water for any purpose for which you would otherwise have used fresh water, then it is a useful thing. We regularly drain off modest quantities of fish tank water which we store in a 200 litre blue plastic drum. While the water is in the blue drum, we are able to add any additional ingredients (like chelated iron) or even a little compost tea. At the same time, we top the fish tank up with fresh rainwater which keeps the water quality parameters within appropriate limits. This integrated arrangement leverages our use of the rainwater and provides us the means to grow a wider range of plants. While virtually any soil- based growing system lends itself to partnering with an aquaponics system, my favourites include: Square foot gardens Raised sheet mulch beds Wicking worm beds Raised Sheet Mulch Beds We first learned about sheet mulch gardening from the Permaculture books written by Bill Mollison and David Holmgren. The benefits of sheet mulch gardening include: There is no need to dig the soil so it is perfect for lazy gardeners or those with physical limitations. It suppresses weed growth It uses much less water than a conventional garden.

3 3 Large gardens can be established with modest effort. Inexperienced gardeners can achieve good results with little more than suitable mulch and a seasonal planting guide. Creating a sheet mulch bed is simplicity itself: Choose a site which receives adequate sunlight and preferably one which is bordered by buildings, concrete paths or fences. This makes it easier to contain the garden. Raised beds are ideal since they resist weeds, provide excellent drainage and are easy on the back. Slash any coarse weeds. Don t worry about removing them simply lay them flat. Spread blood and bone, food wastes or well- rotted animal manure to kick start the biological processes that will result in fertile soil which drains well but which also retains adequate moisture. Cover the bed area with wet sheets of newspaper or cardboard ensuring that you leave no spaces. This hastens the decay of the existing weeds and prevents future weed growth. Spread clean mulch like seaweed, rice husks, sugar cane mulch, dry leaves, straw sawdust or wood shavings to a depth of at least 150mm. Avoid using hay which often contains weeds. If you use wood shavings or sawdust, ensure that you don t bury them as they will deplete the soil of nitrogen. Soak the bed thoroughly and leave to drain for a couple of hours. To plant the garden, part the mulch and use an old knife to cut a slit in the paper. Place a handful of clean soil or compost (or worm castings) into the slit and plant a seedling into the soil. Carefully, draw the mulch back around base of the plant while leaving the leaves exposed. Repeat this as often as you have seedlings that can be accommodated in the bed. It s important to fill the bed up with plants. Diversity is a cornerstone of this system so ensure that you plant different vegetables, herbs and flowers. Keep the bed well- watered during the first few months to encourage the microbes which will transform the soil. Over time, earthworm populations will increase and soil aeration will improve. In the second and subsequent years, the bed will also require less water as the retentive capacity of the soil is enhanced. If weeds appear, part the mulch and lay a sheet of newspaper over the weeds and cover well with more mulch. It s important not to let them get a hold. You should bury vegetable and fruit scraps and other garden residues in the bed to provide plant nutrients. Over time, many self- sown seedlings will begin to appear. Avoid meat or fish scraps which will attract dogs, cats, flies and vermin to your garden. Worm castings are an excellent soil conditioner and plant nutrient source. Maintain the layer of mulch - we use sugar cane mulch and pea straw. It adds valuable nutrients as it rots down, it keeps your fruit and vegetables clean and it reduces water consumption. Our sheet mulch gardens are in four circular raised beds that are 600mm deep and 1500mm in diameter. We used sections of concrete storm water pipe. The benefits of these beds are that they are virtually indestructible and their height makes them what our computer- literate friends refer to as user- friendly. They resist weeds and they need much

4 4 less water than a conventional garden. The concrete sections were half- filled with sandy loam topped off with a mix of nursery potting mix, coco peat and well- composted horse manure. We plant seedlings for vegetables with tiny seeds. We usually sow large seeds directly into the soil. To determine if the beds need water, we simply poke a finger into the mulch. If the mulch appears to be drying out, we water the beds. To summarise, sheet mulch gardening is an excellent growing system and, while it will grow anything, it is of particular interest to us because (given that we produce salad vegetables, leafy greens and soft herbs in our aquaponics systems) it is so well suited to the production of root crops and potatoes. Square Foot Gardening The brainchild of American Mel Bartholomew, square foot gardening is an excellent plant growing system that makes very efficient use of water, space and time. It is particularly useful for people who long to grow their own clean, fresh vegetables but who lack the skills or experience to garden in the conventional way. The key elements of square foot gardening include: Planting in squares rather than rows. Different plants are sown in each square at the rate of 1, 4, 9 or 16 plants per square foot (depending on the plant). The beds are square or rectangular in shape not wider than 1200mm (4 ) for easy access from either side. Narrow beds (in increments of 300mm) may be useful if restricted space and beds can be virtually any convenient length. Provide aisles that allow easy movement around the beds never walk on the beds. Raised beds provide essential drainage and help to keep weeds at bay. They also make for gardening with greater personal comfort - less bending or kneeling. The condition of your soil isn t an issue because you don t use it. Bartholomew recommends a growing mix comprising equal parts of compost, peat moss and coarse vermiculite. We substituted coco coir for the peat moss that Bartholomew recommends - on sustainability grounds. Stagger plantings for continuous harvests. As squares become vacant, simply top them up with some more compost and plant them out again. The use of a planting grid that divides the bed into squares is a cornerstone of the method. Bartholomew claims (and my experience supports) that a square foot garden: Involves 50% of the cost Requires 20% of the space Uses 10% of the water Needs 5% of the seeds Requires 2% of the work

5 5..of a conventional soil- based garden. While Bartholomew recommends watering by hand using water that has been warmed by the sun, we rigged up a reservoir that we filled with water from our fish tank. A small pond pump delivers the water up to the plants. Surplus water drains back into the reservoir. We harvested our first lettuce seventeen days after we planted them out as seedlings. The pak choi became available for use at about the same time. We began harvesting tender silver beet leaves at four weeks and beans at six weeks. Square foot gardening is particularly well- suited to small vegetables or those which can be trellised. We ve discovered that bushy plants like dwarf beans tend to inhibit the growth of adjacent seedlings by denying them sunlight but this can be avoided with a bit of thought about where you plant what. This is an excellent growing system for novice gardeners and for those who lead busy lives. Our use of fish tank water simply extends the efficiency of square foot gardens even further. Wicking Beds For us, wicking beds were arguably the most exciting development in growing systems since we wrote the first edition of this book. Wicking beds are the brainchild of Queenslander Colin Austin. Austin claims that the wicking worm bed is a highly productive growing system which not only produces food from limited water, but also recycles waste organic material to provide plant nutrient and capture carbon. At its most basic, a wicking bed is a waterproof box with a drainage hole drilled a pre- determined distance from the base. A pipe is inserted into the box which is then filled with growing mix. The pipe is used to add water to the box which drains from the hole in the side when it reaches the correct level. In practice, the water in the bottom of the box is wicked upward so that the rest of the growing mix in the box is kept moist. This extends the interval between watering. The addition of hollow structures (like sections of PVC pipe), create reservoirs for the water and extend the irrigation intervals even further. Wicking beds can be constructed virtually anywhere that allows for the creation of this water reservoir..in ground, above ground or in a wide variety of containers. Some variations on the theme feature a worm feeding station (a section of 100mm PVC pipe will plenty of small holes will do) which is inserted into the bed. Chopped food scraps (or animal manure) are placed into the feeding station and are converted to plant nutrients by the worms. Wicking beds have captured my attention for the following reasons: They save water. They provide the plants with continuous access to water and nutrients.

6 6 They can be integrated with other growing systems including square foot gardening. They are very easy to water plants get water from bottom less fungal disease. They are simple and inexpensive to build..and easy to operate. They will go for days (or weeks) without having to add water. How long they can go depends largely on how much water can be stored in the lower section of the bed...and they would partner beautifully with an aquaponics system. The core principles include: Wicking refers to the movement of water (by capillary action) upwards through suitable soils (or other growing mixes) like the movement of molten candle wax along the wick. Wicking beds rely on the creation of a water reservoir of 75mm 150mm deep. A layer of soil (or growing mix) is then added to a depth of 300mm. The wicking action is limited to about 300mm. At the bottom of the bed, the soil is very wet and at the surface only slightly moist. Mulch is added to the top of the bed to minimise water loss through evaporation. Plants should be fed throughout their growing cycle (rather than in one initial hit). The soil or growing mix needs to be maintained at the correct level for optimum growing conditions. If it is allowed to compact too much, the plant roots become waterlogged. Polystyrene broccoli or fish boxes are ideal for conversion to wicking boxes they are cheap, well- insulated and can be set up at a comfortable working height. Fibreglass or plastic grow beds would also make excellent wicking beds. For those who don t mind working on their knees, a wicking bed can be constructed in ground using little more than a sheet of builder s plastic. Wicking beds clearly offer scope for experimentation. There s a need for something fibrous in the mix (to assist the wicking action) so compost would be a desirable inclusion and even coco peat might be useful. One recommended growing mix comprises equal parts of clay, sand and worm castings. Another option might be to use a 60/40 mix of coco coir and course vermiculite. Watering your wicking beds from an aquaponics system would provide some nutrients and liquid fertilisers like Charlie Carp or Seasol would serve as a top up. Overfeeding is a risk in a closed system like wicking beds so you would be advised to feed little and often. Periodic flushing of the reservoir with rainwater would help to avoid problems with any build up of minerals. The inclusion of a worm feeding station is also a good idea. Why not turn those kitchen scraps into nutrients for your plants? Wicking beds demonstrate many of the features of the best growing systems and, as such, they will integrate very well with an aquaponics system. The Best of the Best

7 7 Consider this! While each of them brings their own unique twist, the one thing that is common to square foot gardens, raised sheet mulch beds and wicking beds is their efficient use of water. One day, it occurred to me that I could marry the best features of each system. Set up a wicking bed and add some SFG growing mix and fit a planting grid. Set it up at a comfortable working height. Replenish the wicking bed reservoir with water from your fish tank as required. To summarise...aquaponics is not the only way that you can integrate fish and plants. Using the nutrient- rich water from your aquaponics system to water raised sheet mulch beds, square foot gardens or wicking worm beds will not only expand the range of plants that you can produce...it's actually good for your aquaponics system, too. - o0o-