Drip irrigation and the wetting front can really limit plant available nitrogen and nutrient distribution in saturated soils. Soils need to breathe.
Whenever designing a drip system the first thing you need to decide on is the drippers. Whether it’s do it yourself or commercial I’d first find out the drip tube or dripping system technical information for pressure rating, drip spacing, and flow rate. Pressure is especially important for gravity-fed systems.
To begin with you need to decide if you want Pressure Compensation (PC) drippers to account for elevation change. For every 1 meter of elevation change there is a 9.8 kPa pressure change with it. That 1 meter is 10% of the 100 kPa (1 bar) minimum recommended for most commercial drip tubes. A 10 meter change in elevation may see the highest drippers simply not drip and others just end up blocking because of the low pressure. Assuming sufficient flow rate, drip lines higher in the landscape will see less pressure the higher they are relative to the bottom drip lines where gravity wants the water to naturally run to. Without a high enough flow rate, there may not be enough water to pressurise the top drippers. The length of piping an drip tubes and whether they’re made into a loop also matters as pipes have friction losses and pressure equalisation to take into account.
Most commercial drip tubes should work fine with about 1 bar (14.7 psi, 100 kPa, 10.2 meter head) if they actually get 1 bar. For example this PC drip tube only needs 50 kPa (0.5 Bar) for pressure compensation but recommends 100 kPa (1 bar) minimum. In general, the higher the pressure, the less likely the drippers are to block, but it depends on the dripper and water. Some drippers are designed to oscillate to clear blockages but need pressure to do so, and pressure is often short in supply in gravity-fed systems not designed well.
For extremely low pressure systems or low drip flow rates that resist blockages, you’re better off looking at wick siphon irrigation, which I will cover that at a later date.
Sizing your piping and connectors for flow rate based upon how many drippers you use and their flow rate matters a lot in any irrigation system, but especially gravity-fed where the pressure is generally lower. You must also account for the pipe & connector friction losses mentioned in gravity-fed systems in order to deliver the pressure needed at the dripper.
You can find pressure drop calculators to help you there. Remember that the longer the pipe, the more pressure drop. So if you have to run a long pipe to your garden, it’s always best to go large for gravity-fed. That includes the internal size of the connectors and any fittings. As one simple flow restriction upstream could ruin your plants day.
Now that you know the size of pipe you need to supply the water to the drippers, you have to get that water from somewhere, and here I’m covering a gravity-fed pond system.
A submerged pipe and pond inlet that is floated just below the surface and moved with the water level but prevented from landing on the bottom is one way to then feed a sediment filter without sucking in lots of debris. This can then be fed to a filtration system such that your drippers don’t block. Another way is to use a pond siphon where the piping runs higher than the water level in order to help prevent debris entering.
Many people think using a mesh filter on the inlet is a good idea, however they can be problematic if not well designed. If you do use a plain mesh inlet filter, I’d make the mesh area large and make the mesh the lowest point of the inlet so that when you weren’t watering, anything large sucked against the mesh would drop away. A cone mesh filter with the peak pointing down for example. Cones have larger surface areas!
I can’t help you with pond filter sediment experience, however there are a lot of commercial and homemade designs out there. Ideally you add a pressure gauge before and after whatever filter you use. That way you’ll know if it’s performing as expected, or the pipe leading to it is blocked(likely the inlet). Add a valve before the filter too for maintenance. Personally I’d probably want a large high flow biological filter I never had to clean. I’d make mine a submersible cylinder mesh with multiple cylindrical layers of filter medium, with the inlet in the middle of it. Let the microbes live on the filter medium and clean the water naturally I say. Might be a bit of a bastard getting it into the middle of a large pond though. 🙂
However if that level of filtration or water treatment isn’t enough there are large commercial systems by Puricare that treat water by oxidation to help prevent irrigation blockage. It uses an ozone generator, a UV light and hydrogen peroxide to produce hydroxyl radicals. In India rather than filter or treat they use simple non-pressure compensating button drippers because of high hardness bore (calcium and magnesium) water blocking most drippers, they can be unplugged cleared and plugged back in. There’s also evidence Magnetically treated water can help reduce the build up of these divalent elements in hard water.
Once you have your water, filter, treatment, piping and drippers all worked out, you may want to automatically control their operation. Electronic soil moisture or timer controllers are one option, there are lots of those around and it’s what most people use. Tropf Blumat is a passive system for home gardens and doesn’t need electronics, but I don’t believe they have a commercial version. Evapotranspiration as used in Aqualone and Measured Irrigation are other options.
If you’re really keen on understanding watering check out The Scientist’s Garden.
Know of other automated irrigation systems that don’t require electronics? Please comment.
Others I know of include siphon watering timers where water is dripped into a siphon container and once the water level reaches the siphon outlet it over flows, siphoning water to plants, empties, and then starts the drip timer process again.
Personally I like evapotranspiration controllers like Aqualone. Before I knew about theirs I made one of my own design that’s more redundant, but I’m trying to simplify it to come up with a good design that doesn’t require magnets, or like mine; pressure valves. Ideally I want one that anyone could make that will hold mains (500 kPa) pressure and be easily made by anyone anywhere.
David The Good is in a hurry to help his trees in this one and he inspired an interesting comment by Garden Earth Guy that piqued my interest and so I had to research further.
Here’s Garden Earth Guy:
When I used to manage sports fields and large parks- I would place to magnets on the irrigation line. When the water passes through magnets it creates ions, much like how things green up after an electrical storm.
After a bit of digging I found that this could actually work, with a caveat. It depends on the water harness (calcium carbonate > 50 mg/L) and alkalinity (pH >7.2) of the water source. Seems the divalent ions (Calcium and Magnesium) that make water hard, and whether your soils are also high in these and alkaline, determines how effective this is.
In addition to the Ca+Mg, one drip irrigation study with magnetically treated water also showed phosphorus solubility almost doubled inside the water front, and that suggests an effective pH change toward neutral. Interestingly, with the increase in phosphorus at the edge of the water front (where there’s air) there was also almost a doubling of nitrate compared to control. Nitrate was ~4x higher at the edge than close to the dripper.
So by magnetically treating your water, you’re effectively lowering your Ca+Mg in alkaline soil which brings the soil closer to neutral pH and increases phosphorus availability. Simples.
So if your soil or water is alkaline this should work great for you, but if they’re not, it may do little or in fact be negative in the long term. Measure your soil pH to know.
The effects of magnetic treatment on irrigation water have been studied. We showed that the main effects were the increase of the number of crystallization centers and the change of the free gas content. Both effects improve the quality of irrigation water. As an example, changes in natural water due to magnetic treatment in a commercially available apparatus, Magnalawn 2000, have been studied. On the basis of laboratory and field results, the type and the chemical content of natural water for which a magnetic treatment method is the most efficient have been determined. Our analysis shows that the important components for effective magnetic treatment are flow rate through the apparatus and certain chemical parameters of water, namely, carbonate water hardness of more than 50 mg/L and concentration of hydrogenous ions in water at pH > 7.2. Irrigation with magnetically treated water is the most effective for soils with high soda content.
Results now or your money back!
I’ve often wondered how well fertigating plants simply by mixing soil and water well regularly would perform…
You are after all helping to dissolve soil nutrients into the water for soluble nutrient loving plant roots to take up.
Notice how much soil disturbance this subsoil watering wand creates. The murky water is effectively fertigating the plant and aerating the soil all in one action.
That’s great right?
A while ago, before I knew better, I came up with the idea of using an ultrasonic cleaner filled with water and soil to fertigate with. You ultrasonically shake the soil to bits to dissolve the nutrients and then water it on. Part of me still wants to perform that experiment…
However I have a few concerns with any soil disturbance method. The first includes the break down of organic structure of the soils. You can see clods forming large aggregates on the surface of bare soil in the wand video. This tends to happen in soil deficient in organic matter and also calcium as it leaches away and the clay particles bind to one another. Sulfur and boron among others tend to leach as well.
By constantly destroying the soil structure you destroy microbe homes and the microbial exudates that hold soil particles together. Small colloids that become suspended in the water either then end up together or at the top of the soil and will often create a soil crust or large clods when they dry out. Take a look at the classic jam jar soil shake test below and see what I mean. Up top you have organic matter floating, followed by clay, silt and sand particles at the bottom. That organic matter dries in the sun above a layer of clay and ends up oxidising away into the atmosphere, or if you’re lucky becomes food for the subsurface microbial survivors in that clay. The clay then forms a barrier, water won’t penetrate and instead runs off or sits on the surface and then evaporates.
Heavy rain can also create a similar problem in dispersive soils with mineral imbalances.
Notice how dry the top soil was. It has no structure, no organic matter, it will hold little water. That’s unproductive soil. The most valuable soil, the layer at the edge between air and soil with the most aeration, is going to waste.
That soil could benefit from mulching.
Chop, throw, drop.