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Features - Special Focus // Irrigation

Learn how WaterQual, a new online tool, helps interpret your irrigation water quality testing.

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Figure 2. Surface water sources such as this irrigation pond may require treatment for biological water issues such as algae or plant pathogens.
Photos provided by the authors

Many challenges can result from poor quality of your irrigation water. When using well or municipal supply water, issues mainly arise from high levels of dissolved ions such as sodium, chloride, or bicarbonates. Chemical water problems may require a treatment technology such as reverse osmosis (Figure 1). If you are irrigating from a catchment pond (Figure 2), biological issues such as algae and plant pathogens may require a sanitizing technology such as chlorination. Filtration (Figure 3) is needed with both well and surface water sources to remove particles such as sediment that clog fine irrigation emitters.

Sending in a water sample to a horticulture laboratory for testing is the first step to diagnose a water issue. See the sidebar on how to sample your irrigation water. Tables 1 and 2 provide guidelines on what parameters should be tested.

However, measuring is not management – you need to interpret and act on water test results. For this reason, we designed a free online tool for growers called WaterQual (Figure 4) available at cleanwater3.org/growertools.asp.

Figure 1. Technologies such as this reverse osmosis system may be required to treat chemical water quality issues such as high electrical conductivity.

Enter the results from your water test report into WaterQual to highlight likely problems for use in irrigation in greenhouses and nurseries.

The extension tool is in English and Spanish, and can be used on a desktop or mobile device. WaterQual is a collaboration of the University of Connecticut and University of Florida, with funding by federal and industry partners.

WaterQual interpretation

An example water report from a California nursery is shown in Figure 4. WaterQual highlights several key points for this grower:

Table 1. Chemical water quality measurements *Not interpreted in WaterQual

Moderate pH and high alkalinity: pH and alkalinity levels this high mean pH adjustment (addition of acid) will be required in the spray tank for some pesticides. Injection of acid is recommended to reduce alkalinity and avoid an increase in substrate-pH over time.

Figure 3. There are many filtration options, such as these automatic back-flushing disc filters, to remove particles (“suspended solids”) from irrigation water.

High chloride, and moderate EC and sodium: The high chloride level increases electrical conductivity (dissolved salt level) of the irrigation water and the risk of salt burn of foliage and roots. It may be necessary to have periodic leaching of the root substrate or replacement of a recirculating nutrient solution to avoid salt build up and restore nutrient balance. Treatments such as reverse osmosis or blending with rainwater may be necessary.

Table 2. Biological water quality measurements *Not interpreted in WaterQual

High calcium: Ca is a fertilizer nutrient. Increased Ca can limit plant uptake of other required nutrients such as potassium and magnesium, but fertilizer levels are often as high as 200 ppm. As Ca level increases in the water source, decrease the applied fertilizer Ca.

High total suspended solids: Filtration is necessary, with increasing need for multi-stage filtration to avoid clogging of drip or micro-irrigation equipment as TSS increases. It is also important to know what types of particles are present (biological, chemical, or mineral) in order to select the best filtration option.

Figure 4. Example data in the online WaterQual tool available at cleanwater3.org/growertools.asp.

High levels of aerobic bacteria: The risk of clogging of irrigation equipment is high because the bacteria count is above 10,000 CFU/mL.

We suggest you get your water tested at a laboratory, and try out the WaterQual tool. If you would like more training on water quality and treatment, take our new four-week online course “Water Quality and Treatment” which begins on Nov. 5 2018. See hort.ifas.ufl.edu/training/ for more information on this and other courses. Additional resources are available at cleanwater3.org.

Acknowledgements
This work is supported by Critical Agricultural Research and Extension grant #11947449, the Clean WateR3 Specialty Crops Research Initiative grant #2014-51181-22372, and the Floriculture Nursery Research Initiative grant #58-3607-8-725 from the USDA NIFA, and industry partners in the Floriculture Research Alliance.

About the Authors
Dr. Paul Fisher is a professor and extension specialist at the University of Florida, pfisher@ufl.edu; Dr. Rosa Raudales is an assistant professor and extension specialist at the University of Connecticut, rosa.raudales@uconn.edu; Dr. Bruce MacKay is the managing director of ThomasBaine Ltd., a company specializing in eLearning and decision-support software for the horticulture industry, bruce@thomasbaine.com