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SandponicsTM SM
3D view of the shade house and grow beds
The overview drawing above shows proposed raised grow beds located inside an existing 10-metre long x 8-metre wide x 3,5-metre high shade structure, with an elevated masonry-built or fibreglass fish tank (or multiple tanks) located outside the structure. Detailed, engineering, and installation drawings will be provided later.
I am back on to the Sandponics project (July 2nd 2023) and have now installed a liner and a 13mm diameter drain pipe that has 4mm holes drilled along its length, layed along the length of the bed and exiting the bed at the far end. The hole through the liner where the pipe exits is blocked up with a good amount of bentonite clay to form a watertight seal. Landscape fabric was wrapped around the pipe to help prevent sand from entering. Some grit was then laid over the pipe and covered with more landscape fabric. The bed is now ready for coarse-washed-river-sand to be added to form a water filter. Following which another layer of landscaping fabric will be laid down before adding sandy soil.
8 July. The bed is now filled with sandy soil, and pipework is used to distribute the water and fish waste throughout the bed, meaning that ridges and valleys are not required, thereby providing a greater surface area for planting. I eventually removed the plastic sheet as it was keeping the soil too cold and retaining too much moisture in the soil.
Cross-section view of the grow bed
The diagram above shows the drainage and outlet pipe and the bed of coarse-washed-river-sand, with the bed of sandy soil located above. Fish waste and water are added to the reservoir as a weak solution. This then runs through the upper perforated reticulation pipes and is distributed throughout the bed. The water percolates down through the sandy soil and through the bed of river sand, then out through the outlet pipe.
If more filtering is needed, I will add a second sand filter prior to the water entering the proposed in-ground sump.
The beds could potentially be built in the ground, although that would involve doing some very clever plumbing with the outlet pipe, such as burying an extension pipe that takes the surplus water to a quite deep in-ground sump, which is OK in sandy soil, although may possibly be an issue in heavy clay soils, as the sump may overfill and any surplus water not easily drain away. My conclusion is that raised beds are superior to in-ground beds in all soil types.
October 7 2023
Over the past few months I grew some rocket and leeks seeded directly into the test bed. The rocket grew well, although has now finished and has been pulled from the beds, while the leeks are still growing well, and a few climbing bean plants have also started to appear. Plus, I have added seeds for other types of vegetables to the beds. Of course, seedlings could be grown in suitable trays and transplanted to the sand beds once they reach a suitable size, and this may possibly be a more efficient way to grow some plants.
I have now removed the plastic sheet shown in the original video, as it does not appear to be achieving anything, and was in fact keeping the soil cold and wet. I tested the soil pH a few days ago and found that it was far too low at about 4.5, and so have for the time being stopped adding fish fertilize. The lesson here is to closely monitor and limit the amount of fish fertilizer that is added to the beds in order to control the pH levels in the soil. Also the soil was far too wet, which is an issue because of the current regular rainfall being experienced, and the fact that the bed was a wicking bed that constantly holds some water in the base of the bed. I adjusted the outlet pipe so that no significant amount of water is now retained in the base of the bed.
I will continue to remedy any other issues that may arise as we head into summer. The climate here in Perth, Western Australia heats up and dries out as summer approaches. For example, it is 36 degrees C (97F) today at 12 noon, with low humidity, and so summer is on the way, meaning that the issue of too much moisture in the soil should remedy itself through increased evaporation. I will carefully monitor the amount of fish waste and water that is added to the bed during summer in order to prevent the pH falling too low.
I hope to develop more grow beds and put a clear plastic roof on the shade house before next winter in order to keep the winter rain out and the warmth in, I will also monitor the amount of fish waste and water that is added to the bed over winter. No doubt other adjustments will be required as the project progresses, one of which is that a soil sample needs to be taken and professionally analyzed, so that any required adjustments to the soil's mineral composition can be made, such as the addition of appropriate minerals to remedy any deficiencies that may be identified.
I am now feeling confident that the soil pH, soil moisture, and mineral composition of the soil can be controlled during both summer and winter, and the air and soil temperatures will also be capable of being optimized in order to maintain good growing conditions year round. This will require some planning and testing to achieve optimal outcomes, although I believe it is doable.
Three way meter used to measure
soil pH, moisture, and light levels.
The water level in the fish tanks shown in the diagram is high due to the tanks being above the ground level rather than being located in the ground. This will enable the fish waste from the bottom of the tanks to be regularly flushed out and directed into the sand beds under the influence of gravity, or alternatively directed into a sand filter bed (details still to be determined), in a manner that is controlled by a timer and valve.
If the fish waste were directed into a sand filter, the waste could then be collected from the surface of the filter and composted then dried for later application onto the surface of the grow beds. The now clean water from the filter would drain into the sump from where it would be pumped back into the top of the fish tank. Then, water from a slightly higher level in the fish tank could be directed via pipes onto the sand beds to retain moisture, but without the fish waste. This would help prevent the pipework from becoming blocked with fish waste, and the waste could be composted, dried and powdered, or pelleted. The dried fish waste could possibly be mixed with a small number of suitable minerals and applied to the beds in measured amounts to suit the requirements of the plants being grown in each bed. This is a preliminary thought, that has not yet been fully tested or proven. Of course, various other plumbing arrangements could be designed and built to create an effective system that enables the plants to be watered and fertilised.
The filtered water from the elevated grow beds drains into the in-ground sump, from where it is pumped back into the fish tanks, with a float switch activating a small pump whenever the water in the sump reaches a predetermined level. One advantage of this arrangement is that the pump is only ever pumping clean, filtered water, meaning that there is no danger of the pump becoming clogged with fish waste etc.
The in-ground bed will be about 500 to 600 mm deep (possibly more) in order to accommodate the roots of the fruit trees. In my sandy, free-draining soil, drains similar to those used in conventional wicking beds will be used to ensure the in-ground bed does not become flooded. This may mean the loss of a small amount of water from the closed-loop system as the drain will be too low in the ground to enable any surplus water to be directed back to the sump under the influence of gravity. However, with an effective water management plan in place to suit your local soil conditions, this should only lead to a small loss of water. The raised beds however will drain back into the in-ground sump via 25 mm or 50 mm diameter poly pipes or similar.
A major advantage of the Sandponics system is that once you have built your own system and have it up and running, with a little maintenance it will continue to produce new crops and feed you and your family for many years, and yet you only need to build your system once. Also, you can if you wish help other people, including friends and associates to build their systems, possibly by establishing a demonstration system of your own to display. You may then even be able to develop a viable business promoting and installing new sandponics systems in your region. View the business page for more details.
Additional rain-catchment, water-storage, tanks could potentially be located adjacent to the elevated fish tanks, located under the eaves of the house, and plumbed in to maintain the same water level as the water in the fish tanks. Also, a water level float valve could possibly be used to enable mains water, or water from an elevated storage tank to be introduced to the system to help top-up the water level in the fish tank if and when required.
The two-tiered beds shown in the drawing are based on something called Muti-Storey Gardens that appear to work very well for the farmer demonstrating them, and so we thought we might try to do something similar with sand and fish waste, rather than with manure, in order to see how that works out. The side panels for the multi-tiered beds could be manufactured to a suitable size by using techniques shown in this video and then wire-tied together to prevent them from bulging out when filled with moist sand.
All that is needed now is some sweat, tears, time, and scrapped knuckles to get it built. Although, in the system shown in the above drawing, one 3-metre-long section of one of the raised beds will be developed first to prove that the proposed bed lining method works, before developing other parts of the existing raised beds. Fish-based fertiliser and hand watering will be used to feed and water the plants until the fish tanks and sump are built, plumbed in, and stocked with fish.
Note that sandponics techniques could also be used to help establish free-standing fruit trees or/and street trees by lining a suitable-sized planting hole with an appropriate decomposable liner that will rot away over a specified period of time (possibly a calico sheet soaked in an appropriate water-based solution of Bentonite clay). The planting hole can be filled with suitable media containing appropriate mineral and organic additives, plus a suitable in-ground plastic container water reservoir with a suitably controlled leaky valve designed to release a pre-determined amount of water into the bed over a set period of time. The reservoir and valve can be designed to provide water to the sapling for an appropriate period of time, and the reservoir would only need to be refilled occasionally depending on the local environmental conditions such as air temperature and the species of tree etc. Once the tree is suitably established, the reservoir can be removed and an in-ground pipe installed in its place, through which the sapling can be watered as required during hot-dry periods. Eventually' the sapling will become mature enough to only require occasional watering during summer periods, and may eventually require no watering at all as the tree's roots grow to become large enough to reach down into the soil' to levels where there is always some moisture available even during extreme summer conditions at the surface. Each species of tree will have different watering requirements although these can be calculated, with appropriately scheduled watering rosters designed and applied.
A possible variation of the Sandponics system described above, which may possibly suit some growers and be of value when growing various species of plants is to create a 200mm deep sand filter using coarse-washed-river-sand in the lower area of a 500mm deep sand bed, with a drainage pipe located at the bottom of the bed leading to a drainage sump.
Then, lay a suitable porous membrane on top of the sand filter, and place suitably selected soil on top of the membrane, to a depth of about 300mm. The soil will need to be of a consistency that allows water to drain reasonably freely, while also allowing ridges and valleys to be formed on the surface that will allow water and fish waste from a fish pond to flow evenly in the valleys along the length of the bed, and then down through the soil and into the sand filter layer. Plants are then planted along the tops of the ridges and water and fish waste is applied as previously described.
This variation of the system includes elements of conventional wicking beds, with the drainage pipework arranged in such a manner that some water is always retained at the bottom of the sand filter, while also preventing the bed from becoming flooded. The value of this system is that readily available soil can potentially be used in the upper layer of the bed, while Course-washed-river-sand is used only in the sand filer layer of the bed.
This variation of the system is so far untested, although should ideally function well, so long as care is taken in the type of soil used in the upper layer of the bed, and heavy clay soils and potentially other unsuitable and polluted soils are avoided.
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