Aeroponics - Can plants grow without soil?

jtd · July 14, 2019, 7:48pm

Plants can grow without soil.
The earliest historical records show a hydroponic like cultivation in MExico during period 1150 – 1350 CE.
Morehart, C. (2016). CHINAMPA AGRICULTURE, SURPLUS PRODUCTION, AND POLITICAL CHANGE AT XALTOCAN, MEXICO. Ancient Mesoamerica, 27 (1), 183-196. doi:10.1017/S0956536116000109

More recently V.M.Artsikhovski published in the journal “Experienced Agronomy” an article “On Air Plant Cultures”, in 1911, about his method of physiological studies of root systems by spraying various substances in the surrounding air - the aeroponics method. He designed the first practical aeroponics system.

Soil less plant growth is of much interest for cultivation in space, where every resource transportation involves exorbitant cost.

Soiless plant growth are generally classified as hydroponic, aquaponic and aeroponic.
Hydroponics involves immersion of the rhizosphere in a nutrient rich water solution.
Aquaponics is hydroponics with nutriente being generated by marine life, usually fish, but also arthropods.

Aeroponics uses a spray of nutrient rich water droplets between 5 and 50um directly on to the plant roots.

The advantages of soiless growth include very low waste of water and fertilizer, prevention of soil based infection, increased growth area in vertical systems, cultivation in resource constrained areas, ability to increase photosynthesis by artifical lighting.
Disadvantages are extreme dependency on un interrupted power, plant death if humidity levels are not mainatined for periods as low as 20 minutes, external nutrient supply and the need for good electronic control systems.

An aeroponic system can be setup in a lab for highily controlled plant growth experiments and growing of exotic species.

There are multiple variations on the above methods.

WE will construct two types
Vertical Driponics.
Vertical Aeroponics.

We will use commonly available materials. The goal is to encourage urban farming and experiments, at low cost.
Here is a photo of first prototype:

Vidyut · July 15, 2019, 6:36am

I am interested in this, but can think of several practical modifications for my purposes.

Right off the bat… cool roots. Black tower will cook my collection. But I suspect we could make it out of clay and use only plants that will tolerate clay (several species will flat out die if there is any major root nutrient). Also plants that grow naturally on vertical cliff faces.

What clay… I’d been thinking earthen baked clay, but now I’m thinking “shadu” clay - the stuff they make ganesh idols out of. It holds water brilliantly without losing structure for quite a bit (a DRIP on it will kill it fast, but mist should only make it deliciously cool. Alternatively, a more durable option may be plaster of paris. If we make a design, we could probably make a silicone mould of whatever works and have the ability to churn out new towers in the time it takes for plastic to set.

Then the structure could be made out of a plastic mosquito screening (like they install on windows with velcro) or the bird screening, for some spine, coated on both sides with the clay and appropriate holes made.

This will inevitably result in some roots also gripping the clay or growing into it if it gets softened enough (it will - roots are determined things) and have the added bonus of a “buffer” in case of power failures. Both the evaporation from the clay as well as roots having some ability to absorb from it (like from soil).

For my “cool roots needs”, a modification could be to have a small “channel” of water around the top rim of the structure, which absorbs some of the water from the fogging chamber itself (no separate irrigation needed). This will result in some gravity fed wetting of the whole system, resulting in natural evaporative cooling + said “buffer” against power failures.

Drawback: This limits the plants I can grow in it to those growing on limestone cliffs or I’ll have to do a coat of regular clay on the inside (this may not be feasible - adhesion issues between dried PoP and wet clay - don’t ask how I know…).

What is the media used, or is there no media?

Vidyut · July 15, 2019, 6:45am

Personally, I’d be wary of using this thing on expensive plants without a failsafe that doesn’t depend on electricity. One eposode of “Vasai-Virar under water, no power for a week” would FINISH them even with limited inverter backup.

Easy failsafe I can think of is an overhead tank that periodically gets filled by water collected below. If the PoP wicks water down the sides of the gadget, even in a power failure, the plants would have some humidity at the roots. And whether water is lost by fogging or wicking off by the container, if levels drop, the overhead tank would automatically replenish them. In a power cut, even with fogger not working, a person could at least refill the overhead tank manually to help the plants.

This is also not perfect, but better than nothing. A minor battery backup for just the fogger would be efficient on the battery (as opposed to battery AND pump) and an overhead tank would also allow that extended time backup.

Vidyut · July 15, 2019, 7:08am

But this will defeat the objective of a cheap system…

Maybe I could just experiment with it as it is and see what happens and modify on the fly to meet growing conditions. Or try first with regular vegetable plants.

jtd · October 6, 2020, 7:44pm

Finally got around to setting up aeroponic towers on my terrace.
To hold 4 towers I needed a stand. I decided to build a mild steel stand, Which set off a chain reaction of creating a workshop to weld the stand. Which then required a table. Which has now imploded into creating several mechanical tools - posts to follow - which will also help in other projects. Interspersed with pandemic lock down woes…

Back to aeroponics:

Each tower is made of 20cm PVC pipe and has 5 columns of 8 holes for planting. In a base area of 314 cm^2 (0.348 ft^2), barely sufficient to grow one plant we can grow 40.

Slotted the tower with 8.5 cm slits spaced 15cm apart vertically and 12.5 cm around the circumference. Now heating the area around the slot to create the grow holes. The heat gun is a 2kw hot air gun running at low speed for 150 secs. This softens the pvc. Then insert a conical wooden peg of dia of 4cm ( circumference 13 cm). The wooden peg is actually the foot of an old settee.

Peg inserted into slot.

Grow hole view. Peg removed after the PVC has cooled.

Tower-photo_2020-10-07_01-18-49
Two more columns of holes on the rear to be done tomorrow.

jtd · November 1, 2020, 2:35pm

My earlier attempt of using piezoelectric misters did not have the reliability required to operate 24/7 for 90 days at a stretch. The piezo element is continuously exposed to moisture despite being coated with a water proof rubber glue. The constant 115Khz vibration probably causes glue to detach and create micro pores through which moisture creeps in by capillary action. This leads to failure after roughly 90 days. Which means we have to replace the piezo after every planting cycle. However replacing is difficult and expensive. There is also the chance of failure mid cycle at night, which would kill the plants unless attended to.
Regular agriculture nozzles like this Photo of 3 headed spray nozzle is available. The drawback is the need of a high pressure pump consuming 48 W. However this pump generates pressure of 10.3 bar or 101.97Mtr water column, is sufficient to drive a large number of such 3 headed nozzles. The mist produced - as tested with a single such nozzle - is prodigious. Consequently the duty cycle we will require will be fairly low. When coupled with it’s ability to drive many towers it’s power consumption is comparable to the piezo mister.
Additionally we now have wholly locally produced and easily available - in rural areas - components for this project. Plastic green house cooler nozzles are available too. I have them and will try them out too.
Removing soil places continuous process industry constraints on this type of farming. Which means every component in the water and nutrient delivery chain has to be ultra reliable and have a replacement turnaround time of less than 30 minutes.

jtd · November 1, 2020, 2:39pm

Additionally we need to cultivate nitrogen fixating bacteria to infuse into the water. This should eliminate the need for using nitrates. We will however require P and K along with micro nutrients all in water soluble form and completely free of residue to prevent the tiny nozzle holes from clogging.

Perhaps cubist can rescue us with some viable solutions.

jtd · November 26, 2020, 8:13am

Tower bottom cap.

The elbow fitted to bottom with rubber grommet protrudes on the inside about 25mm. Hence will result in a 25 mm pool of water. This will eventually fill with debris. The debris will clog the nozzle / filter. Consequently some method of periodically draining the tower is needed. A standard drip irrigation nozzle (small grey nozzle in pic) with the spray hole blocked serves the purpose. It protruded on the inside 1mm, which was filed off before fixing. The nozzle dia is 2mm. A hole of 11mm was drilled and filed to 11.5mm. The nozzle was coated with ethylene glue, then press fitted in. The fit was perfect and had no leaks. The nozzle cap is easily unscrewed draining out water and debris. Residual debris can be flushed out with a jet of water from the top of the tower.

The four mounted towers with reservoir and pump

Fixing the vertical pipe to the pump outlet was difficult as the pump outlet is a threaded 16mm nozzle. Appropriate threaded coupler is not available in city shops or online, although it would be easily available in rural areas. Hence a 10cm length of 16 mm pipe was heated at one end, expanded and force fitted on the nozzle. Additionally a screw hose clamp was used to fasten the pipe securely. A elbow was connected to the other end and the vertical arm of elbow was fixed to the vertical pipe.
Pump was switched on. A very good spray was observed. Along with multiple leaks. The worst leak was at the pump nozzle. The screw hose clamp has a flat portion that causes the pipe to be loose just below. The clamp and connecting pipe was removed and the nozzle wound with 12 layers of .03mm PTFE tape. The pipe was refixed and the clamp fixed with substantially lesser force.
The pump is a standard dual motor pump used for spraying purposes on farms. It can be run with one or both motors operational. The difference in droplet size with both motors operational is marginal. Hence only one motor is being used to operate all four 3 headed spray nozzles.

Other leaks at the spray head needed only tightening of nozzles.

Now the tedious task of making 160 net cups from mosquito net mesh.

jtd · December 8, 2020, 6:51pm

Net cups filled with old coir. Rs.10 tap filter on outlet and inlet.
Filters are excellent. In 2 hours of operation nozzles never clogged. But outlet filters clogged with coir residue resulting in water accumulation in tower. Inlet clogged with dust causing pump inlet of soft pvc to pinch.
Switching 30s on-off reduces problem substantially. But inevitably it will clog.
So coir is out and clayballs will have to be substituted.
@TechNife suggested gravity based trapping (say contained overflow pots) help reduce clogging ?
The towers already have a head of 25mm. I was hoping it would precipitate particles. It does not. Probably the falling water causes sufficient turbulence.
@TechNife I feel some centrifugal + gravity based jugaads incorporated into the flow should yield the most interesting affordable automagic reductions in clogging the filters on the main flow paths. Trials & errors I guess continues.
@vvcstemplay " I also suspect a centrifugal input will considerably reduce the problem. Very cheap faucet extensions have nice little plastic fans in them, moulded on a metal pin. Inserting one in the inlet will set up a nice vortex, that should throw the lightweight coir fragments away from the nozzle."
I was about to test the above suggestions including purchasing some filters from Amazon. But lazy me cooked up a new hightech filter. A HoleeGram Filter

A bottle punctured with holes and a sock.

Pipe is fitted in a hole in the cap.
The ensuing conversation on telegram
@TechNife , [08.12.20 19:10]
[In reply to VicKram Crishna]

@TechNife, [08.12.20 19:10]
@vvcstemplay , Is it this ?

@vvcstemplay [08.12.20 19:52]
[In reply to TechNife]
Yes, I also use one like this in the taps. It prevents water splash, by diffusing the flow.

@vvcstemplay , [08.12.20 19:57]
Of course, the coir particles won’t be removed. So, at some point, you’ll either have to redesign the entire tank system so that the excessively particle filled water is led into a wastewater settling tank, or start using either throwaway or washable filters.

The trouble with a simple settling tank is that the pump evidently causes too much turbulence, and the particles don’t settle under their own weight, or else are less dense and will never settle. If the latter, you can’t use a settling tank at all, and must think about a filtration system.

JT D, [08.12.20 20:45]
[In reply to VicKram Crishna]
Dual tank system. Ideally with a recirculating filter pump. The problem is the higher cost.
However the sock holeegram filter is working well. I removed the outlet filters, so all the debris falls straight into the tank. The much larger surface area spreads the particle trapping and the lower speed stops sucking the larger bits which settles down or floats. Tomorrow i will make 4 more for the outlets. I simply punctured holes with a solder iron. Which catches the sock, making removal a irritant. Tomorrow will drill proper deburred holes. So changing socks becomes simple. Even so not very scalable.

JT D, [08.12.20 20:52]
Changing the bottle and sock together is extremely easy. Just unscrew the cap and screw on a second. If it can function without cleaning for several days, it would drastically reduce routine cleaning.

Three hours of nonstop running without problems. Tomorrow I will make 5 proper HoleeGram Filters with deburred holes and fix 4 on the outflow pipes and one on the inflow of the pump.
@Pneb will also add the electronic control to turn on/off the pump and some level control and alarms.
The PSU used is a PC SMPS used to power Intel Atom motherboards. It is a 400W psu and the 12v section can deliver 20A, well in excess of the 6A required when both motors on the pump is running.

GN · December 8, 2020, 7:08pm

This entire narrative is so exciting. It takes so many skills to grow plants when we deviate from the natural way. Each parameter needs to be controlled. Whether we grow food from these vertical farms or not, we will grow lots of knowledge from these epistemological gardens.

jtd · December 8, 2020, 7:47pm

Meanwhile others build the instrumentation to read natures encrypted signals.

Abstract

Precision agriculture requires new technologies for rapid diagnosis of plant stresses, such as nutrient deficiency and drought, before the onset of visible symptoms and subsequent yield loss. Here, we demonstrate a portable Raman probe that clips around a leaf for rapid, in vivo spectral analysis of plant metabolites including carotenoids and nitrates. We use the leaf-clip Raman sensor for early diagnosis of nitrogen deficiency of the model plant Arabidopsis thaliana as well as two important vegetable crops, Pak Choi (Brassica rapa chinensis) and Choy Sum (Brassica rapa var. parachinensis). In vivo measurements using the portable leaf-clip Raman sensor under full-light growth conditions were consistent with those obtained with a benchtop Raman spectrometer measurements on leaf-sections under laboratory conditions. The portable leaf-clip Raman sensor offers farmers and plant scientists a new precision agriculture tool for early diagnosis and real-time monitoring of plant stresses in field conditions.
https://www.nature.com/articles/s41598-020-76485-5

jtd · December 8, 2020, 8:17pm

jtd · December 17, 2020, 4:35pm

The coir used for filling the netcups is a great attraction for sparrows and a huge problem for us. The sparrows yanks dislodges lots of coir strands, several of which fall inside the tower clogging the drain. So we have to replace the coir with baked clay balls. The ball size is 8mm to 15mm and will fall out of the bottom of the netcup. So we use this vegetable packaging net to line the inside of the netcup. Glass beads being used as a test substitute, since clay balls are yet to arrive.

jtd · December 17, 2020, 7:55pm

ATTINY2313 micro running aeroponic pump. Cycle time 30 sec. Duty cycle 50%.
JT D, [17.12.20 18:29]
On the left is a pc psu that powers the board and pump. Pump controlled with relay. Wouldn’t a MOSFET be preferable?

JT D, [17.12.20 18:30]
Timer is interrupt driven.

@Kush_agra_wal, [17.12.20 18:38]
Relay would give perfect isolation between controller and pump hence i guess in this case relay will be a better option and also the selection would depend on how much current is to be switched that depends on pump and i think relay can switch or control more current than MOSFET?

Kushagra Agrawal, [17.12.20 18:39]
Not sure of it👆

JT D, [17.12.20 18:53]
[In reply to Kushagra Agrawal]
True that isolation is excellent. The relay’s inherent isolation is 3.5kv. But PCB layout is very important to achieve that.

JT D, [17.12.20 18:54]
Current draw is 8A. Voltage is 12v.

JT D, [17.12.20 18:56]
There is a rs485 driver so that i can connect to a server like Raspberry PI. Should i use rs232 instead?

Kushagra Agrawal, [17.12.20 19:15]
[In reply to JT D]
But then to draw this max amount of current we would need a high gate voltage to control the switching so it may be possible that micro controller been used won’t supply this through its I/O port? Means again it would need configuration, if possible, to be used?

Kushagra Agrawal, [17.12.20 19:17]
And in this aeroponic farm the data is collected from multiple points or a single point?

JT D, [17.12.20 20:22]
[In reply to Kushagra Agrawal]
Multiple.

JT D, [17.12.20 20:32]
[In reply to Kushagra Agrawal]
To drive the relay we use a transistor. The relay requires 12v. The transistor is TIP122 connected to 12 v. So a gate drive of 12 v is quite feasible. We will save space and have a far longer life for a transistor, but it probably wont save us any money.
design optimisation- cost, space, reliability, manufactureability, serviceability…
If we were making several thousand, it would definitely be a MOSFET.

Kushagra Agrawal, [17.12.20 20:42]
[In reply to JT D]
Then rs485…cause i think with rs232 you can connect only one device. Like rs232 was used with db9 cable for printer and computer connection.

Kushagra Agrawal, [17.12.20 20:45]
And selection would also depend on basis which proto is faster among rs485 and rs232 as data would be transferring.

JT D, [17.12.20 21:01]
[In reply to Kushagra Agrawal]
Yes. RS485 is a balanced line multi drop system.
Speed will be slower than a RS232 as it is half duplex - unless we separate the tx and rx lines. However the amount of data is very sparse. So a very low speed would be perfectly ok.

@Anool jokingly suggested a 555 timer
Anool Mahidharia, [17.12.20 18:54]
[In reply to JT D]
Looking good.
Although, a 555 would have done the job !!

JT D, [17.12.20 19:04]
[In reply to Anool Mahidharia]
. Yes. Unfortunately water level and rs485 link are likely to mess up a 555, though we could implement a 556 level control.

Anool Mahidharia, [17.12.20 19:05]
LOL, just kidding. gotta get in a 55 joke at every opportunity.

JT D, [17.12.20 19:10]
[In reply to Anool Mahidharia]
. But seriously a fully discrete transistor implementation would be fun.

JT D, [17.12.20 19:11]
After all blokes are building cpus with transistors

jtd · December 18, 2020, 5:35pm

We now have a fair indication of evaporation from the 160 grow holes on 4 towers.

The volume of water between the lowest permissible level - pump sucking air - and maximum water level is 2.4 li.
In the morning and evening evaporation is approximately 500ml/hr. Midday it climbs to 1.2li/hr. This is at the current peak temperatures of 30^oC. We thus have a peak evaporation rate of 7.5ml per hole per hour. We now have some figure to calculate transpiration as plants grow.

jtd · December 22, 2020, 8:05pm

First shoot emerges 4 days after planting Vigna_unguiculata aka chouli. This one uses glass beads. Two more have clay balls as the medium. A few seeds planted Yesterday 22/12/2020. Let’s see how many sprout.
The green mesh vegetable packing net is expected today. This will enable the replacement of the coir with clay balls and planting all the grow holes.

jtd · December 28, 2020, 9:49am

5 days later (28/12/20)…

jtd · January 2, 2021, 6:55am

Vigorous growth. Roots are as long as 15 cm inside the tower.
Replaced coir with clayballs inside a wide meshed packing net placed inside the mosquito net cup on one tower. Planted 10 black eyed beans in each. Replacing coir and planting on all towers in progress. Hopefully this task will be completed by today.
Will add NPKM to water once planting is complete on all towers.
Also removed the socks filter on the 4 outlets, leaving it on the inlet only.

jtd · January 9, 2021, 2:48pm

Planted all the grow holes 2 days ago. The general practice is to germinate and grow until a few leaves appear in a nursery bed, then transplant to the tower. However this is a very tedious process as far as I can tell. So we simply threw 10 seeds into each net cup - first some clayballs, then seeds. then cover with clayballs.
Some problems cropped up with the crop. Sprouts have appeared in all holes. However seeds at the bottom of the conical net cup sprouted inside the tower. This is a major problem as there is very little light inside. These sprouts fall into the tower and clog the drain. Approximately 25% of seeds have germinated inside the tower. Which means poor eventual yields. Also noticed that roots growing thru the mosquito mesh net get constricted somewhat. I had kept the bottom and the seam of the cone open. This proves to be a disaster as some of the sprouts simply grow vertically thru the seam gap, instead of following the cone contour towards the mouth. One cannot correct now as pulling out the cups damages the fragile roots. So will grow this for a few weeks and harvest.
One will require a better method of planting to prevent the seeds from dropping to the bottom of the cone thru the gaps in the clayballs. Also direct the roots towards the open bottom of the cone instead of through the mesh.
More to follow…

Vidyut · January 11, 2021, 7:43pm

Fascinating. Looking forward to updates.

If you’re using sprinkler nozzles and recycling water and the problem is water pooling, clogging, etc why not put the sprinklers on a timer and not recycle the water? You can use weaker nutrient mix that will keep your nozzle and pump healthier too. 5 min off, 5 sec on, etc - on a cyclic timer. Time it so that roots are moist but there is very little runoff - discard it. No fuss, no clog. Saves electricity too. Occasionally you can run the mist for a longer time with plain water as a rinse.