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Recap of Cultivate'15 educational sessions:

A closer look at recirculating and treating irrigation water

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 EnvironmentalOutlook 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.”

Plant pathologist Ann Chase at Chase Agricultural Consulting said algae tend to be the biggest problem with recirculating water. The optimum conditions for growing greenhouse crops are the same conditions that allow algae to thrive.
Photos courtesy of Peter Konjoian, Konjoian’s Horticulture Education Services

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,; [email protected].

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.

Biofilm can come into a greenhouse in a municipal water source even though the water has been treated. Schedule-40 polyvinyl chloride irrigation line: new pipe (top), “clear” water line with biofilm (middle), and fertilizer line that carries 200 parts per million nitrogen with layer of algae (bottom).

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, [email protected].

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

6. Ultraviolet light

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.; [email protected]; Sal Mangiafico, Rutgers Cooperative Extension, Woodstown, N.J.; [email protected].

This article, written by freelance technical writer David Kuack, was published at de corporate blog of Hort Americas,

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