Q: Our irrigation water was recently tested and found to be slightly salty. This situation is all new to me. Is there anything we can do considering that this is our only irrigation water source?
A: Good water quality is often taken for granted, but like your soil, irrigation water should be periodically tested to see what is in it. Water may be found unsuitable for a particular use based on selected chemical and biological characteristics. Salts, sodium, bicarbonates, pH and other minerals affect water quality. Water quality is also not static, but may be influenced by a number of situations. For example, pumping and depletion of groundwater can cause saltwater to migrate inland and upward, contaminating the water supply.
Salty water (also called saline water) can cause leaf burn for turfgrasses. Salt water in the soil can pull water from the plant’s roots, resulting in physiological drought stress, even with adequate moisture in the ground. If the concentration of some salts is high enough, there can be a direct ion toxicity to the plant, resulting in poor plant health. Another potential problem from salty irrigation water can be ion imbalances that can result in nutrient deficiencies.
There are also significant negative implications of salinity to the soil. Salty water will degrade soil structure, causing more compaction and reducing pore space for water movement. Without adequate water movement through the profile, surface ponding of water will reduce efficacy of fertilizers and pesticides. The compacted soil profile can also negatively impact the soil’s microbial ecology, which is necessary for good plant health.
The salinity hazard of water is usually expressed as the total content of soluble salts, measured by electrical conductivity (EC) or total dissolved salts (TDS). These units are used to classify irrigation water quality so that management practices can be suggested for different levels of saltiness of the water. At the lower end of the scale, there is usually little concern since periodic rainfall will dilute the salt water. As the saltiness of the water increases, there is an increased need to leach the salts from the soil by using additional water, either from the same source or from a cleaner source. I suggest you contact a water specialist if your water tests above 1,000 ppm total salts. They can determine a leaching program for you to use if needed.
Salts and sodium do not act independently. For that reason, water quality tests will usually measure the sodium adsorption ration (SAR) to determine the ratio of sodium to calcium and magnesium. This ratio will also be used to classify irrigation water and help determine the potential damage sodium will inflict on soil structure and permeability. In general, an SAR value below three is considered very safe for turfgrasses. Water with an SAR of nine will cause increasing structural damage to clay soils and then to sand soils with slightly higher SAR values.
Gypsum is the first line of defense to use for soils with high SAR values. Research has started evaluating other amendments that may be helpful when using poor water quality for irrigation. Some of these amendments may be injected directly into the water and others may be applied to soil. Cultural practices such as cultivation and topdressing can be used to improve soil properties. Ultimately, you will likely need to more closely manage your other inputs to try offsetting any negative influences from the water.
Grady Miller, Ph.D. Professor and Extension Turf Specialist North Carolina State University
Questions? Send them to Grady Miller at North Carolina State University, Box 7620, Raleigh, NC 27695-7620, or e-mail firstname.lastname@example.org
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