By David Kuack
Jerry van Kampen, inside sales support, and Vic Mirabella, sales account manager, at Priva North America Inc. sat down with Hort Americas to talk about greenhouse water issues and water treatment.
van Kampen: Rain water is the best source of water for the greenhouse because it doesn’t have any pathogens or elements that you might not want for your crop. It is a very clean source of water.
1. Is there any one water source that is better for greenhouse irrigation than others?
Some city water comes from lakes and is relatively clean and easy to work with. Some city water might come from wells and it might have some hardness to it. A municipal water source may be the only choice for some growers. Municipal water is treated to some extent so that growers have a relatively clean starting point in regards to a water source for irrigation.
2. What are the most common issues that cause greenhouse growers to look at installing a water treatment system?Mirabella: The water source is one of the major issues that most growers have to look at for installing water treatment. If you don’t have a good clean water source, whether it is municipal, lake, pond, whatever that source is, if it’s not good enough for your crop, you are going to need to look at some kind of water treatment to get it to an acceptable level in order to grow your crops.
The two most common problems that growers encounter are bicarbonates and pathogens. Pathogens can include something as simple as algae or something that is plant specific. The other thing that can occur with a water source is a high level of calcium or some other element that can be toxic to the plants.
A grower who is recirculating his water will want to keep tabs on his water treatment system to be sure that there are no pathogens in the recirculation system. In this case, he should be testing his water at least weekly. Photo courtesy of Priva North America Inc.
van Kampen: Depending on the crop, the type of finish quality a grower wants and a crop’s disease resistance are going to determine how aggressive or how sophisticated a water treatment system a grower will to need to install.
3. How much does the type of crop, impact the need, to install a water treatment system?
The type of crop, starter plants or plugs vs. finished plants, and the length of the production cycle also influence the type of water treatment system. If a grower is producing tomatoes for 10 months, after about eight months he really doesn’t care if there are pathogens in the water anymore because the crop is basically finished. All that is left to do is harvest the fruit on the plants. For that first eight months the grower wants to make sure that the tomato plants are healthy in order to produce the quality fruit he wants to harvest.
If a grower is producing a vegetable crop where the plants are being grown for months, the grower is more likely to recycle his water. This is where he really needs some type of disinfection to kill pathogens so that if there is a disease outbreak it’s not spread throughout the entire greenhouse. It stays where it started.
Mirabella: Water is pretty much the lifeblood of the plants. Most growers in Canada have a recirculatory type system. It’s the same water being used over and over so if there is a disease pathogen in that water it’s going to be spread throughout the greenhouse and eventually work its way through the whole crop. Depending on the type of irrigation system that you have it’s going to impact the type of water treatment system you are going to install.
Normally when growers get into a recirculation system then water treatment usually becomes a higher priority. It comes down to crop and disease resistance. If a grower has a crop, if at the end of the week the water is going to be dumped, and the grower is going to start again with fresh water, he may not look at a high end water treatment system. Because the grower is only keeping the water for a short period of time, he may look at a less cost effective system. If a grower is going to continually reuse the water like with a floating pond for lettuce or the crop cycle is so long that the water has to be in the irrigation system for a long time, then a high end treatment system may be warranted. With a floating pond system there isn’t an opportunity to drain the ponds, disinfect them, refill them and adjust the nutrient levels because those would all add to the cost of production.
4. How much does length of the production cycle impact the type of water treatment system a grower should consider installing?van Kampen: It also has to do with, at what stage the crop is at. When you are talking about starter plants they are prone to be more susceptible to pathogens and less tolerant to high salt levels. With younger plants you are going to need better water or you are going to need someone who knows how to make that water better.
Mirabella: Many growers water test on a regular basis. That is probably crop dependent and also what a grower is looking for in the water. If you have a bad source of water with a lot of bicarbonates or heavy metals, you probably want to keep tabs on your water at the pretreatment system. In that case, you should be testing on a weekly basis if not more often.
5. How often should a grower have his water tested?
If you are recirculating water then you want to keep tabs on your water treatment or water sterilization to be sure that there are no pathogens in the recirculation system. Again in this case, you are probably going to test your water weekly. During the summer when a grower is watering more often, he should consider testing twice a week to keep tabs on what’s in his water, how stable is everything in the water, and what is happening with the water.
Water testing frequency will also depend on the crop you are growing and the age of the crop. If you are propagating in a substrate, then you are probably going to use some type of misting system and injecting a minimal amount of fertilizer. What you are basically trying to do is keep the plant alive, keeping the substrate wet so the roots don’t dry out or get water logged. If you are using city water, you are not worried as much about pathogens. But you are more concerned with what is in the water. Does the water need to be treated to remove or reduce bicarbonates? Does the water need to be treated to lower some element that is in the city water that is too high and will damage your plants?
6. What factors should a grower consider when trying to determine the capacity of the water treatment system?Mirabella: It comes down to the amount of water used in an irrigation cycle. You don’t want to run out of clean water. You also want to look at what is the capacity of your water treatment system. How long does it take to treat enough water to have a day’s worth of irrigation water?
I don’t know if oversizing is necessarily a bad thing for some growers. If a grower is not careful as to how much water he is using in an irrigation cycle or an irrigation day vs. the capacity of his water treatment unit, he could run into under sizing issues. A grower could come up short on having enough clean water for an irrigation cycle.
When looking at something like an ultraviolet system, we look at what is the maximum capacity of water that can be treated and how much can be treated in a day. A grower should look at the limitations of a water treatment unit and use that as a foot print to determine what size operation it supports. Once that size is exceeded another unit is needed.
A 10-acre tomato facility is a fairly substantial size greenhouse. Even if a grower could push it a unit further than that, would he be comfortable knowing if that unit was to fail, a large production area is going to be affected? At that point it becomes a risk management strategy to consider breaking down the operation into smaller chunks with more than one treatment unit. If one unit goes down there is a second unit that can fill in. There may be some redundancy, but if something catastrophic happens to one treatment unit or one area of production, it’s not going to wipe out the whole crop.
Growers are very frugal with their money so they want to stretch every dollar as far as possible. Fortunately, a lot of growers for at least irrigation supply units and fertilizer injector units consider the scenario if they only have one and it goes down then their whole operation is not getting water or fertilizer. By installing two smaller units, should one unit need maintenance or repair, a grower is not completely out of water and can at least rely on the second unit to irrigate his plants.
7. When installing a water treatment system, what factors do most greenhouse growers overlook?van Kampen: As this applies to filters, what normally happens is that a grower will look at the filter spec sheets. The manufacturers will provide best case scenarios. If the spec sheet for a filter indicates it will handle 80 gallons per minute that is basically when the water has already been filtered through it.
If I am buying a filter that says it will handle 80 gallons per minute and I am taking water out of a stream that has a lot of particulate matter in it, I will probably be lucky to get ¼ of that amount of water through it. In this situation the grower is going to need to oversize his filter system to take care of the situation. Even if a filter is sized to handle 80 gallons per minute, if the water is relatively dirty then a grower may have to quadruple the size of the filter or maybe do the filtering in steps. The first step filters out everything that is a certain size and then the next filter will take out even smaller particles so that the filters don’t get plugged up.
Mirabella: No matter what filter or water treatment system a grower purchases, there is maintenance associated with it. The equipment only works at its optimum when the maintenance is done on a regular schedule. Some growers may think because they have a filter they don’t have to do anything else. Most water treatment system equipment has a maintenance schedule and it should be adhered to strictly to make sure the system operates at its optimal capacity.
For more: Priva North America Inc., (903) 562-7351; http://www.priva.ca.
David Kuack is a freelance technical writer in Fort Worth, Texas; email@example.com.
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