When does irrigation water need to be treated?

Having a dependable supply of quality water is critical to producing a good crop, whether that crop is plugs or finished plants, ornamentals or vegetables.

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.
1. Is there any
one water source that is better for greenhouse irrigation than others?

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.

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.
3. How much does
the type of crop impact the need to install a water treatment system?

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
of a water treatment system a grower is going to need to install.

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.
The type of irrigation system a grower is using will impact the
type of water treatment system he will install.
Photo courtesy of Eden Farms Inc.

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.

5. How often
should a grower have his water tested?

Many growers water test on a regular schedule. 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.

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.
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.
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 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 a push 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 pulling 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; dkuack@gmail.com.

Visit our corporate website at https://hortamericas.com