As pressure on fresh water supplies increases, more
growers will look at recycling their water. Recycling water can add a whole
range of challenges that growers may not have had to deal with before. Speakers
at this year’s Cultivate’15 discussed some of the issues growers may face when
recirculating and treating irrigation water.
By David Kuack
As drought conditions worsen along the West Coast and
wildfires scorch many parts of the country, water continues to be on the minds
of the public, government officials and water regulating agencies. Environmental
disasters like the recent wastewater spill from an abandoned Colorado gold mine
into the Animas River also add to the concerns about water availability and
water safety.
Organisation for Economic Co-operation and Development (OECD)
reports in its “OECD Environmental Outlook to 2050: the Consequences of Inaction”
the demand for water will increase globally by some 55 percent. This increase in
demand will come primarily from manufacturing, thermal electricity generation
and domestic use. The report said “groundwater depletion may become the
greatest threat to agriculture and urban water supplies in several regions.”
Challenges of
recirculating water
As more growers look to save water by collecting
irrigation runoff and recirculating their water, the chance for issues with
soluble salts, pH and disease pathogens can be expected to increase. Plant
pathologist Ann Chase at Chase Agricultural Consulting told Cultivate’15 attendees
during her presentation "Meeting the Challenges of Recirculating Water" that use of automatic watering systems has increased watering efficiency, but
in some cases, these systems have also led to less monitoring of crops on a
daily basis.
She said algae tend to be the biggest problem with
recirculating water. She said the optimum conditions for growing greenhouse
crops, including warm temperatures, high humidity and applying fertilizer in
irrigation water, are the same conditions that allow algae to thrive in many areas
of a greenhouse. Many algae also move with water. It’s common in greenhouses to
see algae growing on concrete floors and aisles, benches, evaporative cooling
pads and even on the surface of growing media.
Chase said a major reason many disease fungal pathogens
can thrive in greenhouse conditions is they are “good” saprophytes that don’t
require plants to survive. These water-loving and water-tolerant fungi have a
wide host range. They produce many spores quickly and the spores are motile
making it easy for them to move through water. These spores are also long-lasting
which allows them to wait until conditions are optimum for them to germinate on
host plants.
Chase said growers have a lot of choices when it comes to
how to recirculate and treat their water. She said before deciding on what
water treatment should be used, growers should first lower the rate of
fertilizer they are applying and incorporate a filtering system.
“Filtering has to be done before any type of water
treatment,” she said. “Depending on how fast the water is needed and the volume
of water required will help to determine the type of filtration and treatment
system that should be installed.”
For more:
Chase Agricultural Consulting, http://www.chaseagriculturalconsultingllc.com; archase@chaseresearch.net.
Algae-biofilm relations
During his presentation on “Water enhancement and
hydroponics,” Peter Konjoian, president of Konjoian’s Horticulture Education
Services, discussed the relationship between algae and other microorganisms
living in water. He said if algae are present, one should assume fungi,
bacteria, and viruses may be as well.
“Algae and bacteria produce biofilm,” Konjoian said.
“There is symbiotic relationship between algae and biofilm. These organisms are
highly evolved and highly adaptive.”
He said biofilm can provide algae with enough nutrients
that algae do not need the light necessary to produce these nutrients. Because
of this relationship, algae can grow in water pipes, even in pipe buried
underground.
He said biofilm can come into a greenhouse in a municipal
water source even though that water has been treated. While algae can establish
themselves on a wide range of surfaces inside a greenhouse, it is the
irrigation system that can help promote their growth. If a line is dedicated
solely for fertilizer, even if that pipe is buried underground, algae can
become established.
Konjoian said one of the common irrigation system design
flaws made by growers is they do not provide enough filtration. He said the
mesh size of the filter system needs to be able to filter out particles of at
least 50 microns.
For more: Konjoian’s
Horticulture Education Services, peterkfes@comcast.net.
Water treatment
options
Don Merhaut, associate extension specialist for ornamental
and floriculture crops at the University of California-Riverside, and Sal
Mangiafico, environmental and resource management agent at Rutgers Cooperative
Extension, discussed “Water treatment options for irrigation and tailwater recycling.” The researchers said there are five basic steps to recycling and
treating water:
1. Collection of water runoff.
2. Removal of floating debris.
3. Removal of suspended particulate matter, including
organic matter, clay, sand and silt.
4. Sanitation treatment for pathogens.
5. Control of fertilizer levels.
If irrigation runoff is going to be collected into a
collection basin, the size of the greenhouse or nursery and its water demands
have to be considered.
Merhaut said plant pathogens, including Phytophthora and
Pythium, are usually present in runoff water and irrigation water that comes
from surface water sources. The method of water treatment chosen by a grower
will depend on how clean the water is, the level of sanitation a grower wants
to achieve, the type of recycling system and local regulations.
Mangiafico said the method of fertilizer injection is
usually one of the last things determined because of the impact water
sanitation treatments can have on some nutrients. Some treatment methods may
denature fertilizer chelates suspended in water or remove nutrients from the
water. He said the smaller the container size that is being used to produce a
crop, the more a grower needs to be concerned about micronutrients that are
sensitive to poor quality water.
Merhaut and Mangiafico said the most common water
treatment methods include:
1. Chlorination
2. Slow sand filtration
3. Rapid sand filtration
4. Membrane-mediated filtration
5. Heat
7. Ozonation
8. Copper ionization
The two researchers advised growers, depending on which
treatment method they were interested in, to first try out a small pilot system
before investing in and installing a full scale treatment system for an entire
greenhouse or nursery operation. Once a treatment system has been installed, it
should be inspected and tested on a regular basis to ensure it is operating
properly and is providing the sanitation results expected of it. Records should
be kept of any type of maintenance, parts replacement, etc. that are done on
the system in the event that any problems occur.
For more: Don
Merhaut, University of California, Department of Botany & Plant Sciences,
Riverside, Calif.; donald.merhaut@ucr.edu; http://plantbiology.ucr.edu/people/faculty/merhaut.html.
Sal Mangiafico, Rutgers Cooperative Extension, Woodstown, N.J.;
mangiafico@njaes.rutgers.edu.
David Kuack is a freelance technical writer in Fort
Worth, Texas; dkuack@gmail.com.
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