Almost everything a greenhouse crop receives, it receives through the irrigation line. If that water carries a heavy microbial load, or if biofilm builds up in tanks and pipes, the trouble shows at the roots and then on the balance sheet: uneven watering, blocked emitters and filters, and a higher risk of disease moving through the system.
Ozone is one of the tools growers use to treat irrigation water. Buying a generator is the easy part, though. Good results depend on how the system is designed around your water, how it is monitored, and who supports it afterwards. This guide looks at ozone in greenhouses: how it is used in irrigation, where its limits are, and what to get right before you invest.
Where ozone fits in greenhouse irrigation
Ozone is a strong oxidant. For water treatment it is generated on site, from air or oxygen, and dissolved into the water through a gas-liquid mixing system. It is unstable and cannot be stored, so it is made on demand, where it is used.
Ozone breaks down into oxygen. How quickly depends on the water: warmer water, a higher pH and more dissolved organic matter all make it disappear faster. That means it does not linger the way some chemical disinfectants do. It also means the dose reaching the far end of a long pipe run is lower than the dose at the injection point. And because ozone reacts with whatever is in the water, by-products can form, so treated water should be checked rather than assumed to be clean.
Cleaner tanks and lines
Tanks, pipes and drippers slowly collect biofilm, a slimy layer of microorganisms attached to surfaces. Biofilm can shelter pathogens and it contributes to blockages. Partly blocked lines mean uneven watering: some plants get less water and fewer nutrients than others.
Dosed and monitored correctly, ozone can reduce the microbial load in the water and help limit biofilm from forming. It can also help loosen deposits that have already formed. Results depend on the dose, the contact time and the condition of the system, and heavily fouled lines may still need cleaning and flushing. Because ozone decays quickly, check that the treatment is reaching the parts of the system you are trying to protect.
Waterborne disease, especially in recirculating systems
Irrigation water can bring plant pathogens in and carry them around, and the risk is greater wherever drain water is reused. Ozonated irrigation water can help control waterborne pathogens such as Pythium and Fusarium in recirculating systems, because it reduces the number of viable organisms in the water ahead of the crop. How well it works depends on the organism, the dose, the contact time and the quality of the water.
Recirculating systems reuse drain water instead of running it to waste, which can cut water and fertiliser use. The other side of that is that whatever gets into the system circulates through all of it, which is why water hygiene matters so much there.
What ozone does not do
Ozone works on the water rather than on the plant. Improving the quality of irrigation water lowers the chance of bringing disease into the growing system or spreading it around, which matters most in operations that recirculate water. It won’t, however, clear an infection that is already established in the soil, the substrate or the plant itself. Those cases call for proper diagnosis and ongoing monitoring, so that the right treatment can be chosen.
For that reason, ozone works best as one part of a wider crop protection approach rather than a replacement for it. Growers tend to get the most from it when it sits alongside good irrigation management, hygiene, suitable rootstocks and biological control. If biological products are applied through the irrigation, it’s worth dosing them downstream of the ozone treatment point so they aren’t exposed to ozone.
Research into how plants themselves respond to ozonated water is still developing, and the effects seem to vary with crop, dose and frequency. For now, our designs focus on what ozone does reliably, which is improving the quality of the water your crop receives.
Where to treat: design considerations
Treatment point and nutrient solution. Ozone can oxidise some of what growers add to the water, including iron chelates such as Fe-EDTA and some micronutrients. A common design approach is therefore to treat the water before fertiliser and chelate dosing. Where drain water is returned, the return flow can be treated in a dedicated circuit, and the nutrient solution is then checked and corrected before it is reused.
Borehole water. If the source carries iron or manganese, ozone oxidises these metals so that they can be filtered out. That is one more reason to treat ahead of fertiliser dosing.
Summer conditions. Warm water holds less dissolved oxygen, and a warm recirculating nutrient solution can run short of oxygen at the roots, which stresses the crop. Warm water also makes ozone decay faster, so dose and contact time need to be set for peak-season conditions. Ozone decomposes to oxygen, so ozonation may add a little dissolved oxygen, but it should never be relied on in place of aeration or oxygenation. Measure dissolved oxygen in the root zone through the summer.
Humidity. Greenhouses are warm and humid. Moisture in the feed gas can damage corona-discharge ozone generators, so generator placement, outside the humid growing area where possible, and feed-gas drying belong in the design from the start.
Monitoring and calibration
Before treatment, record how much water flows through the system, its pH and temperature, and what is in it. Organic matter matters most, because it sets the oxidant demand: how much ozone the water will use up before any is left to do useful work.
Once the system is running, measure:
- Dissolved ozone
- Contact time
- Any ozone residual remaining where the water reaches the crop
Redox potential (ORP) readings are a useful indicator of trends, but they are not a substitute for measuring dissolved ozone directly or for testing the water microbiologically.
Calibrate the dosing to the system. Too much ozone can injure roots and foliage, change the nutrient solution and harm beneficial microorganisms. Too little will not give the treatment you are paying for.
Safety and local requirements
Dissolved ozone in an enclosed irrigation circuit is a different matter from ozone gas in the air. Ozone gas is harmful to breathe, and greenhouses are places where people work. The generator, gas lines and mixing system should be designed so that no ozone gas is released into the growing area. Where off-gas is produced, it needs to be vented away from people or destroyed; ozone destruct units convert leftover ozone back to oxygen. Ozone gas can also damage plant foliage.
Requirements differ between sites and uses. Check the local requirements that apply to your operation, including occupational exposure for staff and water discharge, and anything that governs the products you use on crops. Ask your supplier for documentation, clear operating instructions and technical support.
Measure savings, don’t assume them
Cleaner lines and even irrigation can make water and nutrient delivery more consistent, and that may give a grower room to fine-tune fertigation. But ozone does not take the place of fertiliser, and a lower input is only worth keeping if the crop shows it can hold.
Before and after treatment, record water and fertiliser use, other treatments, saleable yield, quality and what each kilogram costs to produce, for each production unit. Check the results against water and nutrient analyses and harvest records, and reduce inputs gradually, not in one step. Using resources more efficiently is what makes the practice sustainable.
Every crop and system needs its own protocol
A dose or result that works for one crop cannot be assumed to work for another. Lettuce, tomato and strawberry, for example, are grown differently and will each need their own protocol. The same goes for the growing system: soil, substrate and soilless systems differ in how water is applied, drained and reused, so the assessment starts with your system and your crop.
Training and support
Equipment alone does not deliver results. The people running the system need to be able to read water quality data, adjust the treatment, check that it is working, and know when to reduce it or switch it off.
Talk to an engineer before you invest
Biozone has been in business for 25 years. We are a South African engineering company that designs and manufactures water treatment systems for agricultural, industrial, commercial and remote applications. We start with your water: its source, composition and flow, and the crops it serves. We then help you define the treatment point, a monitoring plan and the training your team needs.
Request an application assessment with a Biozone engineer
It’s free.
Call +27 67 972 2169 or +27 11 791 4403 · [email protected] · www.biozone.co.za
