What’s In Your Irrigation Water?

Part of a good food-safety plan for your farm includes making sure the water source you use for irrigation is contaminant-free.

by Dani Yokhna
PHOTO: iStock/Thinkstock

Water is one of the pillars of life. Mother Nature doesn’t always provide water at the right time or volume, so farmers rely on irrigation to keep the circle of life in rotation.But not all water is created equal. As farmer of fruits and vegetable, you need to know exactly what you’re using to quench your plants’ thirst. Water quality can influence the survival, production and safety of your food crop.

Test Your Water

Many a farmer has paid the price—literally—by not testing water before irrigation. The best place to start is to ask your local cooperative extension agent for guidance on how to collect your samples and where to send them. Samples generally should be collected from each water source you’re planning to use for irrigation. Underground wells, streams, rivers and ponds are all viable water options. Municipal (treated) water results be checked annually and well water should be checked bi-annually, while surface sources should be checked three to four times during the growing season.

Clear plastic bottles are best used for collecting samples. An 8-ounce baby bottle will do the job quite nicely. When collecting a water sample, run the pump for about 20 minutes and rinse the bottle thoroughly with the running water before taking the sample. Label your sample and include the date. Mail your sample to the lab as quickly as possible so the water maintains its properties.

Here are some things you’ll want to look for on your water-test results.

1. Salt Levels

What’s in water that could be bad for plants.The primary consideration for irrigation water quality is salinity, which is the total amount of dissolved salts in your water. Salts are natural components of the environment that enter water sources through weathering rock and minerals or by proximity to oceans. Storm runoff and leaching of chemical fertilizers and other human sources can also elevate salt levels in water.

High salinity can directly affect the plants’ ability to take up water. Poor water absorption means poor plant performance and reduced yields. Each plant has its own tolerance level, so research your target crop. Tolerances are quantified in parts per million or as a measure of electric conductivity. If your water’s levels are outside of the plant’s tolerance, you can calculate an estimate of percent yield.

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2. Sodium Levels

Red flag No. 2 is sodium loads. Unlike salinity that hinders plants, sodium causes problems with the soil. As sodium works into the soil column, it binds with various particles, making soil impermeable and stifling water infiltration. Clay soils are particularly vulnerable to sodium loads. The sodium absorption rate (SAR) is the proportion of sodium to the calcium and magnesium in your water, and represents the primary measure in a water test. If your water source is high in sodium, calcium- and magnesium-dense soil amendments can mitigate the effects.

3. Toxicity

Finally, a host of elements can be toxic to plants. One of the most prominent is boron. Ironically, boron is essential for plant growth at low levels, but it can quickly become toxic at elevated levels. Crops have a variable range of tolerances to boron, so you must match crop type to your test results. Other toxic elements include aluminum, arsenic, copper, lead and selenium. Review your water test closely for these elements and evaluate the ramifications for your chosen fruit or vegetable.

Avoid Contamination

Food safety has been a growing issue over the past decade. Pathogens and biological contaminants have found their way to the grocery store, particularly in fresh fruits and vegetables. The more prominent contaminants include E. coli and Salmonella. Most human health incidents have derived from fecal coliforms related to animal or human waste. These have been directly linked in fertilizer manures or indirectly through the contaminated water including irrigation. Fortunately, there are a host of strategies you can deploy to mitigate risk.

  • Know Your Land: First, become aware of the land use in your watershed. Is your stream or pond influenced by high rates of animal production? Are clean water conservation practices, like fencing cattle from streams, filter strips and grassed waterways in place? Learn your watershed and encourage sound water-quality management in your community.
  • Know Your Irrigation System: Critically evaluate your irrigation system. Using municipal water tends to be the accepted best practice, but establishing a well with a periodic testing program is good secondary choice. Try to avoid surface water sources, particularly if livestock are a prominent feature in the landscape. Always keep your irrigation system pest proof when stored over the winter. Consider using drip or furrow style irrigation systems, which minimize direct water contact with the crop. If you must use foliar spray systems, then consider stopping irrigation within a week of harvest.

A sound irrigation program can take the gamble out of crop production. Water throughout the growing period will maximize production, but only if you have the right water! Put in the extra effort to make sure you’re getting the best out of your watering program and guarantee your produce is safe to consume.

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About the Author: John Morgan owns a hobby farm in central Kentucky, where he raises a garden with his family. He’s a certified wildlife biologist with degrees from Penn State and the University of Georgia.  

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