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Irrigation water testing and interpretation

By Dr. Justin Quetone Moss & Chrissie A. Segars

Whether it’s your first day on the job or your 20th year as a sports turf manager, it’s important to know where your irrigation water comes from. Common irrigation sources for sports turf managers include, but are not limited to: surface water, groundwater, municipal water, and recycled/effluent water. Now that you know your water source, what in the world is in it and what does it mean? Irrigation water management is an important component of a successful sports turf management program. Whatever your water source, it is important to test your irrigation water so you can successfully manage your field in the best way possible. This article seeks to educate sports turf managers on how to properly take a water sample and what to do once you get your irrigation report back from the lab.

Collecting the sample

Obtaining a proper sample is the first step in receiving an accurate irrigation report. Below are general guidelines for collecting a sample. You should always check with the lab where you are submitting your sample for their specific guidelines. The steps below are taken from the soil, water and forage lab at Oklahoma State University.

  1. Obtain a clean, opaque 4oz water bottle from a local extension office.
  2. Take the sample directly from the irrigation source you want to test (irrigation head).
  3. Fill the bottle halfway, rinse the bottle entirely then pour it out. Repeat three times.
  4. Collect the sample.
  5. Label bottles immediately.
  6. Fill the bottle as full as possible with the lid tight and submit to county extension office or lab.

Interpreting the report

When you first receive your irrigation report, it can be overwhelming. Where do you start? What should you be looking for? Below, we will look at several parameters that will give you a great start for interpreting your water results. All parameters are important, but these are the best place to begin.

pH is the measurement of dissolved hydronium ions in solution. Irrigation water can be classified as alkaline or acidic based on the pH value. The pH values can range from 0 to 14; 7.0 is neutral, below 7.0 is acidic, and above 7.0 is alkaline. A desirable range of pH for most turfgrasses is 6.0 to 7.0 but most irrigation water will range from 6.5 to 8.4. The suggested range is also dependent upon your soil type. A pH outside of this range may not be a direct problem itself, but may show a need for evaluation of other chemical components in the irrigation water.

Bicarbonate & Carbonate are common components of irrigation water that can have a direct effect on turfgrass health. If bicarbonates are >120 ppm and carbonates are > 15 ppm and sodium is >100 mg/L, then there is potential to create sodic soil conditions. This is bad for soils and for turfgrass performance. High concentrations of bicarbonates and carbonates with high calcium and magnesium can lead to deposits of calcium or lime. Irrigation water with a high pH (>8.0) often contains higher bicarbonates.

Residual Sodium Carbonate (RSC) allows us to find the sodium hazard of our irrigation water. To get this parameter bicarbonate, carbonate, calcium, and magnesium are calculated based on an equation and expressed to give us the sodium hazard. An easy way to think about this parameter is calcium and magnesium act as a “blocker” of sodium accumulation. If the RSC becomes too high, the calcium and magnesium are removed and unable to stop the accumulation of sodium.

Electrical Conductivity & Total Dissolved Solids. Saline soil conditions are one of the more common issues when dealing with marginal to poor irrigation water quality. Electrical conductivity is a measure of the degree that a water conducts electricity across 1 cm of water. Electrical conductivity is measured by passing an electrical current through the water sample and recording the resistance. Electrical conductivity is used to estimate total dissolved solids by multiplying by 0.64 based on the units given below in

The Sodium Adsorption Ratio is generally used to determine the ratio of sodium to calcium and magnesium in soils, which determines sodium status and permeability hazard. Although, this is a soil parameter, it can be used to classify irrigation water and is typically reported on irrigation reports.

Total salts

Together, total salts and SAR are used to help predict water infiltration rates. Infiltration refers to the soil’s ability to allow water through; also referred to as soil permeability. Infiltration rates can be improved by high total salts, but high salts may also reduce turfgrass health. Therefore, irrigation water with high salts can benefit and damage turfgrass simultaneously. Extremely pure water can lead to reduced infiltration, even at low SAR. High total salts can help with infiltration at medium to high SAR (15-20); high calcium and magnesium can counterbalance effects of high sodium.

Example irrigation water reports

Let’s look at two example reports. Both reports will come from the Oklahoma State soil, water, and forage lab. These irrigation reports are broken down into categories that make it easy to see and know what to look for. These reports also include a paragraph that gives recommendations based on the reported values. This will not be the case for all labs, but is becoming more common.

The pH of this water is in the upper part of our desired range. However, a pH of 8.4 will still allow for successful turfgrass growth without further remediation. A pH above 8.0 can cause higher bicarbonates, but in this case, since sodium is not an issue it should be suitable for turfgrass growth.

The bicarbonate of this irrigation water is slightly above the threshold of 150 ppm. However, levels of carbonates and RSC are well within the low hazard category. The pH of the water could be the cause of the slightly higher bicarbonate level. Irrigation water with these reported values should have no concern for sodium accumulation.

The EC for this irrigation water falls into the “Excellent” range. This range suggests no management concern. Remember, EC is an indirect measurement of salt accumulation but can still be useful for management considerations.

The total salts reported value of 336.7 ppm falls into the “Good” range for irrigation water. This water should have little management concern especially with rainfall and leaching ability. The SAR of 1.5 also falls into the “Good” range. This value is of little management concern, however, if sodium should become a problem, gypsum can be used to help remedy the concern.

Now that we have looked at these two parameters separately, let’s look at how they will affect infiltration rates together. When used together, these parameters fall into the “Moderate” category for infiltration. If this water is being used on a heavy soil system where leaching is unable to occur, a problem could arise in the future. However, with regular rainfall and leaching occurring, no problem should be found.

Overall, this irrigation water should be suitable for turfgrass growth without many problems, especially if it is on a sand based system.

The pH of this water is in the upper part of our desired range. However, a pH of 8.3 will allow for successful turfgrass growth without further remediation. A pH above 8.0 can cause higher bicarbonates. However, in this case, sodium is an issue but is likely not due to pH.

The bicarbonate level of this irrigation water is well above the recommended threshold of 150 ppm. The carbonate level is below the recommended threshold of 15 ppm. However, when the bicarbonates, carbonates, calcium, and magnesium are used to calculate the RSC, it presents an issue. The RSC is calculated as 3.2 meq, which falls into the “High Hazard” category for sodium accumulation. The higher concentrations of bicarbonates and carbonates have removed a lot of the calcium and magnesium that allows for high sodium accumulation.

The EC for this irrigation water falls into the “Good” range. This range suggests little management concern, especially if rainfall and leaching can occur. Remember, EC is an indirect measurement of salt accumulation but can still be useful for management considerations.

The total salts reported value of 865.2 ppm falls into the “Good” range for irrigation water. This water should have little management concern especially with rainfall and leaching ability. The SAR of 5.1 also falls into the “Poor” range. This is cause for concern. Management recommendations are aerification of the soil followed by sand topdressing, pelletized gypsum, continued soil monitoring, and leaching when possible.

Now that we have looked at these two parameters separately, let’s look at how they will affect infiltration rates together. When used together, these parameters fall into the “Moderate” category for infiltration. Infiltration rates should not be a problem on well-drained soils. Soil management cultural practices should allow infiltration when using medium textured soils.

Overall, this irrigation water is of low quality. The use of this water must be monitored closely and is really only recommended for more salt tolerant turfgrasses on very well drained permeable soils and medium textured soils with careful monitoring. This water is not recommended on heavy soils.

Summary of Discussed Irrigation Parameters

As a sports turf manager, irrigation water quality is very important to understand. As we have learned, interpretation of water quality parameters, while complex, can be done if we follow written guidelines. While management of irrigation water can be done using general written guidelines, some instances may require more in depth analysis. Many factors contribute to proper management as well as problems that may arise. Factors such as climate, soil type, and turfgrass cultivar/use must be taken into consideration when problems or management remedies are concerned.

Dr. Justin Quetone Moss, is associate professor and Chrissie A. Segars is a PhD Candidate, Oklahoma State University.

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