My presentation on irrigation water quality

Yesterday I taught a seminar about irrigation water quality.

Here are some links related to that presentation.

Field day poster: 5 grass varieties, 3 levels of salinity, and a month to grow-in -- or not

This poster for today's field day describes what happened when we planted five grass varieties as stolons and then supplied irrigation with different amounts of salt in the water. I think two things might surprise you. First, some of the grass varieties, including a particular manilagrass (Zoysia matrella), can reach full coverage in about one month after planting. Second, irrigation with salty water, so long as enough is applied, doesn't slow down the growth of many warm-season grasses.

image from

When the grasses can grow like this, it shows that managing the problems with water quality are closely tied to the quantity of water supplied. I will be talking more about this tomorrow when we are back for another day of seminars.

After 28 days, grow-in and salinity differences


I've been growing grasses in a plastic house with a lot of help from colleagues at the Thailand Institute of Scientific and Technological Research (TISTR). The idea was to see how these grasses grow in after being planted as stolons, and to see what happens when salt is added in the irrigation water. I'll be discussing this experiment at the field day in Chonburi next week.

The picture above shows the grasses that receive the irrigation with 330 ppm total dissolved solids (TDS), 28 days after planting. The seashore paspalum looks the best, and the nuwan noi manilagrass has grown-in almost as fast. The hosoba korai, which is a beautiful grass once established, still hasn't covered much of the pot.

Another thing I've found interesting is measurements of salinity in the soil with the new TDR-350. All the pots are supplied with the same quantity of water. But different sets of pots get different amounts of salt in the water.


The soil salinity in these pots is changing depending on which irrigation water is applied. That's just as expected.

For more about the TDR-350, see this webinar.


Grow-in potential

These pictures were taken 28 days apart. Here's what the grasses looked like yesterday, on February 24. That was 4 weeks, exactly 28 days after planting.


On 27 January, five different grass varieties were planted from stolons. The grasses, shown from left to right, are:

  • manilagrass (nuwan noi)
  • tropical carpetgrass (yaa malay)
  • seashore paspalum (salam)
  • manilagrass (hosoba korai)
  • bermudagrass (Tifway 419)

For the first 10 days after planting, all the grasses were irrigated with 330 TDS (total dissolved solids, in units of ppm) water. For the next 18 days, the grasses shown above were irrigated with 4,500 TDS water.

The planting rates for the stolons ranged from 99 g/m2 for the nuwan noi to 312 g/m2 for the yaa malay. This is the mean mass for the stolons planted in the pots. We cut the stolons into 10 segments with 3 nodes each and then weighed them and planted them; each 0.02 m2 pot was planted with 30 nodes (1,500 nodes per square meter).

This is what the pots looked like immediately after planting, on January 27.


I think this is interesting for two reasons. One, this gives some indication of the grow-in rate (and relative rates) of various grass varieties. Second, this shows the tolerance or not of the grasses to different salt levels in the water.

One set of grasses is getting water with salt (TDS) at 330 ppm, the one pictured are getting 4,500 ppm, and another set are being irrigated with 9,000 ppm.

I'll be talking about this, and showing some of these grasses, at the upcoming Sustainable Turfgrass Management in Asia conference.

Read these articles, but disregard the subtitles

When I saw there was a new article at Golfdom about sodium causing agronomic challenges on sand putting greens, I clicked the link to see what this was about.

That link took me to the article by Obear and Soldat in which they explain that sodium does not cause agronomic challenges in sand putting green soils:

"Sand putting green soils have low clay contents and are therefore unaffected by sodium ... The findings from this study suggest that sodium will not negatively affect putting green soils with low clay content, including those constructed to USGA recommendations ... In the case of sand-based putting green root zones, which often have very low clay content, increasing exchangeable sodium percentage well above the standard sodicity threshold of 15 percent had no effect on hydraulic conductivity."

But the link is, which seems the opposite of what the article is about. Sodium causes agronomic challenges for sand putting greens? Maybe if the sand putting green is made of clay.

That reminds me of the subtitle for the article Frank Rossi and I wrote about the Park Grass experiment for the Green Section Record. One of the things I thought was amazing was how soon the botanical composition on the Park Grass field changed in response to fertilizer treatments. We wrote about that in the article, quoting Lawes and Gilbert from their first paper on the botanical composition of the experiment, published just a few years after the first treatments were applied:

"the plots had each so distinctive a character in regard to the prevalence of different plants that the experimental ground looked almost as much as if it were devoted to trials with different seeds as with different manures [fertilizers]."

The fertilizer treatments began in 1856. We didn't put these quotes in the article, but it is clear the effects were noticed immediately. More from Lawes and Gilbert:

"So striking and characteristic, indeed, were the effects produced in this respect, that, in 1857 and 1858, the subject was thought of sufficient interest to induce us to request the examination of the plots by Professor Henfrey, to which he kindly assisted.

An endeavour was also made in the second year, 1857, to separate, and determine, the proportion of the different plants in carefully averaged and weighed samples, taken from the several plots as soon as the grass was cut."

So I was surprised that the subtitle of our article, when I saw it published, was Sometimes the value of a turfgrass management practice takes a long time to become apparent. That's not quite what we were trying to say.

High soluble salts, K, and extractants

Earlier this year Brad Shaver and I had a discussion about salinity and extractants.

I had written previously this post explaining that a saturated paste extract is not a good way to look at soil nutrients and that it is not a good idea to look at a saturated paste extract and compare it to a standard soil test.

Brad asked about potassium (K) in saline soils, about acid extracts overestimating exchangeable K in saline soils, and alluded to a continuing confusion about the combination of high soluble salts in soil, potassium, and different extraction methods.

I’ll explain this in two ways. First briefly, without all the details.

Saturated paste (I’ll abbreviate as SPE for saturated paste extraction) is not useful to evaluate K in soils with high soluble salts because the problem with saline soils is too many soluble salts. The solution to this is leaching of the salts. The K measured by the SPE will be deliberately leached, and depending on how saline the soil is, a large portion of the K measured by a standard soil test, because it measures soluble and exchangeable K, will be deliberately leached as well.

Because one is going to deliberately leach soluble salts from a saline soil, as part of the standard management of saline soils, it doesn’t make sense to use the soil test K, from any extraction method, to determine how much K to apply as fertilizer to saline soils.

What does make sense? There will be some K in the soil. There will be some K added through irrigation water. And in a saline situation one can supply K as fertilizer in the quantity that the grass can use, disregarding the soil K and the K added in irrigation water. This guarantees the grass will be supplied with more than enough K, and one doesn’t need to test the soil for K at all.

Now explained the second way, with a few more details, and some data.

The purpose of soil testing is to determine if an element is required as fertilizer, and how much of that element should be applied. Or, in the case of salt-affected soils, the purpose of testing is to identify the problem and to determine what actions should be taken to solve the problem. Of course, if there is a problem with soluble salts, and one leaches them, it doesn't make sense to try to make a fertilizer recommendation from something one is going to be removing from the soil.

There are two forms of plant-available K in the soil: soluble and exchangeable. A SPE measures the soluble K and a small amount of exchangeable K. A standard soil test, such as the Mehlich 3 or normal ammonium acetate extractions, measures the soluble K plus the exchangeable K. Both the SPE and the standard soil test measure the soluble K, and the standard test will additionally measure exchangeable K.

Here are data from nine sites with the electrical conductivity of the saturated paste extract (ECe) labeled as (ec), the K in ppm by SPE labeled as (kh2o), the K in ppm by Mehlich 3 labeled as (km3), and the location of the sample.

ec kh2o km3 location
4.5 59.0 89 Thailand, fairway
17.4 110.0 118 Thailand, fairway
0.2 6.8 51 Philippines, green
0.1 4.4 215 Philippines, fairway
0.2 10.5 82 Philippines, green
0.3 14.8 55 Philippines, green
0.3 17.1 74 Philippines, green
0.9 45.0 174 Thailand, green
0.9 20.8 38 Philippines, beach

I've marked the ECe = 4 dS/m level with a red line, to show in which cases a soil would be considered saline, and in which it would not. Note that one will try to maintain a site-specific ECe depending on the species being grown and the irrigation water salinity -- the 4 dS/m level is included here as a reference level. These samples represent a range of soil salinity levels, most not saline, and two of them saline. Let's look at what happens with soil K across this range of soils and salinities.

Kh20_vs_ecThe K extracted by SPE, which I have labeled as KH2O to indicate it was extracted by water, is low when the ECe is low, and it increases when the ECe is higher. That is to be expected, because the quantity of soluble K is expected to be a function of the soluble salt content of the soil.

Now we can look at the Mehlich 3 K (KM3) for these same samples.

Km3_vs_ecThis looks a bit different, as it should, because the Mehlich 3 test is measuring both the soluble K and the exchangeable K. When the soil salt content (the ECe) is low, then the KM3 is going to be influenced by the cation exchange capacity of the soil and the quantity of K on the exchange sites, and when the ECe is high then there will be a greater proportion of soluble K as part of the the K measured by Mehlich 3.

This next chart demonstrates that. In each of these samples, the KM3 is a larger value than the KH2O. That is because the Mehlich 3 test measures soluble and exchangeable K, while the SPE test measures only the soluble K. By looking at the difference between the KM3 and the KH2O, we can see that the more salt there is in the soil, the smaller the difference is between these two quantities.

Difference_km3_kh2oIs this making sense? When salt in the soil is low, which is what we want, there tends to be a big difference between the quantities of K extracted. As the salt in the soil increases, the difference gets small, because the quantity of soluble K is very high compared to the amount on exchange sites -- at least in a sandy rootzone.

Slight tangent for a moment -- this is something I've written and talked about before, as something that one should not be bamboozled by.

One wants to have low soluble salt content in the soil. When there is low soluble salt content, it is normal to have a large difference between the water soluble and the exchangeable nutrients. But that doesn't mean the grass won't be supplied with enough nutrients. From Environmental Chemistry of Soils (McBride, 1994): "Ion exchange reactions at surface sites exposed to solution are extremely fast."

Back to the data, now looking not at the difference between KH2O and KM3, but the ratio between them. Remember, KM3 in these data is always larger than KH2O, because KM3 contains both the water soluble (KH2O) and the exchangeable K.

Kh20_vs_km3_by_ecWith this proportion, when it is close to 0 (on the y-axis), that means the KH2O by saturated paste is only a small amount of the KM3. At low soil salinity, that's just what we see. And with increasing ECe, as expected, the proportion of soluble K increases.

This can also be represented in a linear relationship for these data by showing that same proportion of $(K_{H2O}) / (K_{M3})$ across the natural logarithm of ECe.

Kh2o_vs_km3_by_log_ecFrom this chart, it seems that knowing ECe and KM3 is enough to predict KH2O. Not only is the KH2O value not useful in making a fertilizer prediction because one will try to leach it away with the other soluble salts in a saline situation, but it can be predicted from other measurements, meaning it isn't adding any new information.

Managing salt by leaching

Selection_010My turfgrass talk column in the May-June issue of GCM China explains how to calculate the amount of irrigation water to apply when one is trying to keep the soil salinity (ECe) from exceeding a threshold value.

The article is available in both Chinese and English.

If the salt is not leached, and accumulates in the soil, the grass can die. To prevent the accumulation of salt, more water than the grass can use must be applied. This causes leaching as the extra water moves below the rootzone, carrying some salt with it.

Good drainage is essential when salt in the irrigation water requires leaching to be done. In the photo below, there is a low area below the drain, and salt accumulation in the soil at that spot prevents grass from growing.


For more on this topic, see the preceding article in this series: Do you know how much salt is in your irrigation water?

Do you know how much salt is in your irrigation water?

Selection_084My column in the March-April issue of GCM China is about salt. The salt in water is invisible, so one needs to test the water to find out how much salt is in it.

As I wrote in the article, water with total dissolved solids (TDS) of 800 ppm would add 56 g salt/m2 (11.2 pounds salt/1000 ft2) in a 2 week period if irrigation is applied at 5 mm/day. Being aware of how much salt is in the irrigation water is the first step in determining if leaching will be required.

Is sodium an imaginary problem?

On sand putting greens, it is. The problem caused by sodium is a reduction in the downward movement of water in soils. This is caused by the deflocculation of clay in the soil. It is a real problem in soils with appreciable amounts of clay, and in those soils, an exchangeable sodium percentage (ESP) of 15% or more is indicative of potential problems. The solution? Add gypsum to reduce the ESP, and add water to leach the sodium.

But in sand rootzones, what happens when there is a high ESP? Obear and Soldat wrote about this in their recent Soil Science paper, Saturated Hydraulic Conductivity of Sand-based Golf Putting Green Root Zones Affected by Sodium.

Selection_041In this experiment, they constructed 6 sand rootzones, with 5 with amendments, and 1 without. The sand was mixed with each amendment in a 4:1 ratio by volume -- 4 parts sand, 1 part amendment.

  1. Nonamended sand
  2. Sand + peat humus
  3. Sand + Profile
  4. Sand + sphagnum peat
  5. Sand + silt loam
  6. Sand + loam

Then, "the soil cores were placed in plastic tubs and allowed to equilibrate for 48 h in a range of solutions of differing ratios of sodium chloride, calcium chloride, magnesium chloride, and potassium chloride." These solutions ranged in sodium adsorption ratio (SAR) from 0 to infinity, including two solutions with high sodium (37 mmol/L and 185 mmol/L, respectively) and no calcium, magnesium, or potassium.

After these equilibrations in solutions of different SAR, each of the soils had some cores with ESP < 15%, and some with ESP > 15%. How did the sodium influence the saturated hydraulic conductivity (Ksat) of the soils? It didn't do much, except for the sand mixed with loam, which had a clay content by weight of 4.8%. In the unamended sand, sand mixed with peat, or Profile, or silt loam, increasing ESP did not reduce Ksat. In fact, in the unamended sand, the Ksat actually increased after the soil was equilibrated with high SAR solutions.

These are some key results:

In the case of sand-based golf course putting green root zones, which often have very low clay contents, increasing ESP well above the standard sodicity threshold of 15 had no effect on Ksat.

The application of soil amendments for remediation of sodic soils (e.g., gypsum) would only be warranted for sodic soils with higher clay contents and may not provide significant infiltration benefits to sand-based golf course putting greens.

This study also provides evidence that increasing exchangeable Mg2+ [magnesium] does not affect Ksat of sand root zones.

For more about imaginary problems in turf maintenance, see:

The importance of irrigation water testing

Brad Burgess wrote:

I would appreciate your thoughts and comments re this water test. I just read your PACE Turf Article and thought I would run this by you. It could be a nice study for you re salt tolerance in Zoysia …

Never seen water this bad before and tested it after the fact. 

Others have said this water is not even suitable for Paspalum … 

Look forward to your comments. Also attached some photos … at 90 days after planting.

This water had electrolytic conductivity (EC) of 1.4, pH of 9, calcium at 4.7 ppm, magnesium 3.7 ppm, and sodium 314 ppm.

I responded:

Thanks for the photos and the water test.

Photo of turf at the site being grown-in with this irrigation water.

The grass looks great. And that is a pretty poor water. It would be an interesting site to do some tests.

My thoughts on the water -- the 2 most important things to look at are total amount of salt (EC) and SAR [sodium adsorption ratio]. 

EC is what one looks at to see the effect salt in the water is going to have on the grass, how that may accumulate in the soil, and how much extra water will be required to keep the soil salts at a level the grass can tolerate.

For the salt content, it isn't too bad. The leaching requirement [for more about leaching requirement, and how to make these calculations, see this handout] for zoysia using that water, if I use a soil EC tolerance level of 8 ds/m, is 0.037, so the amount of extra water required is minimal, ET / (1 - 0.037). But if the soil structure would deteriorate, then one couldn't leach to maintain the soil EC at 8, and then the salt would damage the grass. As a comparison, the irrigation water at [golf course name redacted] has had 4 times as much salt as this water, and Tifeagle can still be maintained to a high level, as long as one leaches properly.

SAR is what one looks at to see how the sodium may cause a problem with soil structure.

I think [this lab’s water test is flawed] because it does not provide the SAR directly, forcing the customers to calculate it themselves, while emphasizing [less relevant data]. 

For this particular water, the SAR is about 26, which is especially bad for soil structure, especially because the water doesn't have a high salt content. One expects the regular use of this water to cause problems with soil structure (unless it is a sand rootzone) over time, exhibited by slowing of water infiltration. This problem can be addressed by regular applications of gypsum. The amount of gypsum to apply is based on the amount of sodium added in the water, or based on the ESP of the soil. Gypsum can be applied at pretty high rates, like 200 to 400 g/m2. I make a rough calculation that for every liter of water added, one should apply 1.5 g gypsum/m2 to prevent soil structure problems. So if 150 mm of water were added in a month, that would be a 225 g/m2/month gypsum requirement.

To summarize, I'd be concerned about soil structure with this water, would apply 1.5 g gypsum/m2 for each L of water that was applied, with that being done to prevent soil structural problems (disregard that advice on a sand rootzone), and I would make sure that slightly more water was applied than ET, to prevent salinity problems.

I’d like to emphasize three things.

1. It is really important to test the irrigation water. Because Brad had this water tested, he can identify and prevent potential problems. What is in the water is invisible. Many sites have water that is perfectly fine, and a test will confirm that. For locations with high salinity or high SAR, that problem is invisible in the water, until there are visible problems on the turf, and by then it is way too late.

Seashore paspalum has died at this site where salt has accumulated in the soil. This problem can be prevented by knowing what is in the water and then carefully managing the salinity through leaching.

2. Make sure the water is being tested for the right things. One needs an irrigation water suitability test. A comprehensive guide for this is Harivandi’s Interpreting Turfgrass Irrigation Water Test Results. In that, he writes:

When irrigation is applied to the soil, the best indicator of sodium effect is a water’s Sodium Adsorption Ratio (SAR), a value which should be provided in all laboratory water analyses. 

3. If for some reason SAR is not reported, one can calculate it from this equation:

\[SAR = \frac{Na}{\sqrt{\frac{Ca + Mg}{2}}}\]


SAR is sodium adsorption ratio

Na is the sodium concentration of the water in milliequivalents per liter

Ca is the calcium concentration of the water in milliequivalents per liter

Mg is the magnesium concentration of the water in milliequivalents per liter