Quality in question

The transition from winter to spring marks the critical time when agricultural professionals must begin thinking about the state of their irrigation water. Failure to accurately assess the levels of dissolved organic and inorganic substances and develop a strategy to mitigate any systemic problems will directly affect plant health, nutrient uptake and even irrigation system performance.

In his 48 years of working in irrigation water quality and issue mitigation, Cliff Fasnacht, president of Pacific Purification, a Salinas, California-based manufacturer of commercial and industrial water treatment systems, stresses a core truth: The appropriate approach depends entirely on the specific application. Fasnacht stresses “depends,” because there is no universally applicable solution for horticultural or agricultural growers. Water-quality strategies must be tailored to the irrigation method (drip versus pivot), the crop, and regional climate and geography.

“If we’re talking about overhead sprinklers or we’re talking about drip [irrigation] in a greenhouse setting, then all of those applications are viewed differently,” Fasnacht says. “If we’re looking at water for spraying insecticides, herbicides and so forth, then that’s another part of the equation. And what part of the country are you growing in? Unfortunately, there’s no one-size-fits-all answer.”

No matter the variables, growers must prioritize fundamental water-quality principles and parameters to mitigate potential risks to crop yield and irrigation system performance.

Establish a baseline

Brigham Young University Professor and Certified Professional Soil Scientist Bryan Hopkins, PhD, says managing irrigation water quality involves two primary considerations: preventing or minimizing water-quality issues and, more commonly, mitigating issues with the available water. While many areas — including the Western United States — have adequate water quality, he says it is important for growers to understand that plants, much like people, suffer from subtle salt and mineral imbalances.

“The first thing I tell people is how critical it is to test water quality and be aware of [salt content],” Hopkins says.

Fasnacht agrees, adding that a comprehensive initial analysis is the mandatory first step, using the analogy of a doctor ordering blood work to diagnose a patient’s illness. Growers must determine what is in their water and soil to ascertain whether these two factors are complementing or compromising crop health.

There are two ways to monitor salt content in water, Hopkins says. The first is to measure the total mass of solids dissolved in the water, or total dissolved solids (TDS). “High TDS increases water density and buoyancy, like in the ocean, the Great Salt Lake or the Dead Sea,” he says. “You can’t sink anything because there’s so much salt dissolved.”

The other testing method is to measure electrical conductivity (EC), which provides a fast, accurate proxy for total salt concentration. It’s the analysis most agricultural and turfgrass labs typically use, Hopkins says. “It’s the dissolved salts that conduct electricity, so pure water is a poor electrical conductor,” he says. “So, measuring EC provides a reliable, indirect measure of salt content [in irrigation water].”

“The goal is to monitor the salt concentration in the soil, the environment where the plant roots reside, and to ensure that this level remains within acceptable, nontoxic limits.”
— Bryan Hopkins, PhD, professor and certified professional soil scientist, Brigham Young University

Certain salts in modest concentrations, such as calcium and magnesium, are actually beneficial to soil structure. Overly pure water, according to Hopkins, can cause the soil to disperse or “fall apart.” However, excessive salinity in irrigation water is a toxic hazard to crop health.

“Salt is a necessary component of life, and all plant fertilizers are essentially salts, meaning they are good in moderation but harmful in excess,” Hopkins says. “Consider excess road salt used in winter. It’ll kill plants near driveways and sidewalks if it’s not rinsed — or leached — out by spring rains.”

Again, Fasnacht emphasizes “depends,” because municipal water is not the norm for horticultural and agricultural irrigation. Groundwater (wells, springs and aquifers) is a more prevalent source. Growers may also draw from surface water sources (streams, ponds, canals, reservoirs or drainage runoff), the quality of which can fluctuate greatly, influenced by seasonal runoff and drought.

Therefore, both Fasnacht and Hopkins recommend growers conduct a thorough test to determine the baseline parameters for salts and other minerals. Doing so establishes the essential reference point for all future management decisions and evaluations.

“Without that baseline [test], the grower won’t be able to accurately assess the impact of the water on their soil, plants or irrigation system,” Fasnacht says. “And it’s important in tracking changes in water quality over time.”

Hopkins adds that he considers soil and water testing a “package deal.” He explains that the soil acts as a chemical and physical buffer for the root zone. If salinity levels in the irrigation water are slightly elevated, the system will remain stable, provided the soil’s salt levels are kept low through sufficient rainfall and drainage.

“However, [the testing] data is important,” Hopkins says. “The goal is to monitor the salt concentration in the soil, the environment where the plant roots reside, and to ensure that this level remains within acceptable, nontoxic limits.”

According to Hopkins and Fasnacht, the required frequency of subsequent testing, however, is entirely conditional and determined by the water source. For example, a stable groundwater well typically requires only an annual test after the initial comprehensive analysis, ideally performed before the irrigation season. These results are then compared year-over-year to proactively detect significant quality changes.

“If the quality remains consistent, less frequent sampling may be acceptable,” Fasnacht says. “However, environmental factors, such as a flood or major weather events, could affect the groundwater quality and would necessitate additional unscheduled testing.”

Hopkins adds that a standard practice is to test the soil annually and test water up to three times per year, adjusting the water-testing frequency as necessary for source variability.

“Every grower must approach water treatment and monitoring on a case-by-case basis, evaluating the program based on their specific, individual operational and environmental conditions.”
— Cliff Fasnacht, president, Pacific Purification

In contrast, sources utilizing surface water require much more frequent vigilance. According to Fasnacht, this is because surface-water quality naturally fluctuates due to seasonal changes in rainfall and environmental conditions, often changing drastically from spring to summer to fall.

Because of these pervasive variables, Fasnacht says, “the only consistent element is inconsistency.”

“There are no universal guidelines,” he adds. “Every grower must approach water treatment and monitoring on a case-by-case basis, evaluating the program based on their specific, individual operational and environmental conditions. Vigilance is crucial, particularly if a grower notices a decline in crop production despite consistent soil conditions. Water quality may be the factor.”

Management strategies

If water-quality issues persist, particularly high salt levels, remediation efforts must be considered, Fasnacht and Hopkins say. These may include blending in freshwater or leaching soil with large volumes of water to adjust salinity levels; improving subsoil movement with drainage systems; switching to high-efficiency irrigation technology, such as drip or micro-sprinklers; adding reverse osmosis desalination; or adding amendments (such as gypsum or sulfur/sulfuric acid) to the soil to encourage drainage and leaching.

However, some of these corrective measures could become cost-prohibitive for the grower. When finding a lower-salt irrigation source or blending in cleaner water is not an option, sound crop management strategies become essential for grower success.

One critical consideration is plant selection. Plants exhibit a spectrum of salt tolerance. Both Fasnacht and Hopkins advise growers to consult with their local university extension offices and crop science experts for key insights on regional water-quality history, trends and data, as well as appropriate crop selection.

One of the most important management strategies is to avoid letting the soil dry out. Traditional watering advice often encourages slight drying to force deep root growth, allow for oxygenation and reduce disease pressure. However, in high-salt conditions, Hopkins says this practice is dangerous because, as the soil dries, salts concentrate and push salinity in the root zone to toxic levels.

“I used to work on a research farm, and we had super-high-salt water, and we were growing things there that, according to the textbooks, you’re not supposed to be able to do,” Hopkins says. “Part of our success was, one, picking the right cultivars, and two, we kept [the soil] wet.”

Mike Zawacki is a Cleveland-based journalist and frequent contributor who has covered various aspects of the green, horticultural, sports turf and irrigation industries for the last 20 years.