Conventional nutrient guidelines: explaining what I mean by "broken"
Why is the grass so good, but the soil test results so bad?

We have had our water tested and would like a little interpretation

I received an e-mail asking for some help with interpreting an irrigation water test. Since many people may have similar questions, I'll paraphrase the questions here, together with my response.

  1. Is salt the sodium, chloride, and salinity together? Actually, salt on a water test is the total salinity, that is, all the dissolved salts, so it will be sodium and chloride and potassium and nitrate and magnesium and sulfate and calcium and ammonium and so on. And for any irrigation water test, I suggest consulting Dr. Harivandi's Interpreting Turfgrass Irrigation Water Test Results. In fact, this is on my list of Five Articles Every Greenkeeper Should Read. Another great reference is the Irrigation Water Guidelines document from PACE Turf.
  2. What is the difference between SAR and adjusted SAR on a test? The SAR is the number to look at. I disregard adjusted SAR. The adjustment attempts to predict future sodicity problems by considering what chemical reactions may occur in the soil. But it also overestimates the hazard. For a bit more about this, see What's in the water from the University of Nebraska and this abstract from Obear et al..
  3. On our test it shows alkalinity expressed as bicarbonate is 89 mg/L. Is this a problem? No, that is a normal amount of alkalinity. I should add, this is not something that one even needs to check. I spoke about this in a presentation entitled Soil and Water Management: three problems, three solutions. The handout, here, explains how to check the two things that do need to be checked: salinity and sodium hazard.
  4. Do you use ppm or mg/L? These are the same thing. One mg per L is also one part per million.
  5. What does TDS mean? TDS stands for total dissolved solids. It is a measure of the amount of salt in the water. If one would evaporate all the water from one liter, the remaining mass of material is the total dissolved solids, or TDS.

It is important to understand the impact salt in the water can have on the grass, and how that salt should be managed. If it is not managed, the results can be disastrous. 

Salt from the irrigation water has accumulated in the soil, killing seashore paspalum turf on this golf course fairway near Bangkok.

Of course, in many cases there is no problem with the irrigation water. It is still good to know what is in the water, and to be able to interpret the results, because when the turf is good, one doesn't want to damage it in any way.

The manilagrass and creeping bentgrass at this course near Tokyo are irrigated with water low in salinity and with a low sodium hazard.

And in many cases, there may be a shortage of water for irrigation. In that case, one also needs to know exactly what is in the water, and how it may affect the grass and soil. That is the only way to ensure that this limited resource is used most efficiently.

When a limited amount of water is available for irrigation, it is especially important to know what is in the water and how it may influence the grass and soil.

I'll recommend again, print a copy of Interpreting Turfgrass Irrigation Water Test Results and keep it within easy reach. And the Irrigation Water Guidelines from PACE Turf is another good reference that is useful in understanding test results and identifying (or more likely, eliminating) possible problems.


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