# Interpreting Soil Test



## binarboy (Jun 29, 2021)

I got new Tall Fescue sod (Marathon II) installed about 7 weeks ago, and I got the results of a soil analysis test from Waypoint and am trying to figure out how to interpret the results. I understand that the pH is on the high side, and I could try to reduce that overtime with Citric Acid. Iron is on the low side, and I could try to apply FAS to increase that. The Sodium (Na) and Sulfate Ext look high, but I'm not sure what to do about them. N and K look ok, but P is a little low so I could use a fertilizer with some more P. Not sure what that would be though.



The grass is still in a good condition and I'm looking to maintain it and improve it over time. Location is Southern CA (Orange County), so it's mostly dry and in the 70's and 80's.

Thanks for any help or advice you can provide!


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## robjak (Mar 31, 2020)

from G-Man's Soil Remediation Guidelines https://thelawnforum.com/viewtopic.php?f=24&t=15165

I would think that TTTF would grow fine at 7.4 but lowering a bit would always be advisable.

Nitrogen: Use Ammonium Sulfate - AMS (21-0-0) at no more than 4.7lb/ksqft/month as the nitrogen source will also help due to a slight acidifying effect.

Phos: Monoammonium phosphate (MAP) 11-52-0 - Apply at 2lb/ksqft, but account for the nitrogen being applied at 0.22lb/ksqft. It will slightly decrease the pH. 
OR Triple superphosphate (TSP) 0-46-0 - Apply at 2lb/ksqft every month the soil is growing

Not sure if you can locate AMS (21-0-0) or (MAP) 11-52-0. i can get (MAP) 11-52-0 but have yet to find AMS (21-0-0). You lawn is small enough that you could buy online.

Gypsum may help for high sodium. I cannot help with the sulfate.


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## Virginiagal (Apr 24, 2017)

Did Waypoint make recommendations?

Starter fertilizer has a good amount of phosphorus.

I would be concerned about the sulfur being so high. From what I've read, excess sulfur applications generally don't cause a problem. But here is an article saying high sulfur levels in the soil can decrease oxygen levels:
https://www.turfdietitian.com/2019-7-14-nutrient-of-the-month-sulfur/

It may be that your region naturally has high sodium and sulfur because it's dry and sodium and sulfur don't get leached out much by rain. So irrigation is something that would help. Is there a local extension office you could consult? I think you need local advice. Maybe you can figure out why the sulfur level is so high.


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## Ridgerunner (May 16, 2017)

It appears that you have an irrigation issue. See if you can access an analysis of your tap water from your provider. S, Na and salinity are all irrigation related. Your results don't include OM, what's the texture of your soil (sandy, clay?)
An Olsen P value of 21 is good. You can apply a pound of P2O5 from a started fertilizer for maintenance purposes (monitor levels with future testing) but you should break that application up in 2 or three applications spread over the season to help keep the P more available and lessen the probability of it interfering with the availability of other nutrients.


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## binarboy (Jun 29, 2021)

Thanks very much for getting back to me. Waypoint didn't make any recommendations, but I contacted them today and they said they will. So I will wait for those.

Thanks for the suggest about the analysis of tap water as well. I will look into that and get it analyzed. The texture of the soil is clay, and I'll look into P2O5 fertilizer as well (not familiar with it, as this will be my first application of fertilizer).

Again, thanks for the recommendations and hopefully Waypoint has something to say as well, and I will be looking into my irrigation.


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## LeeB (Jul 1, 2019)

Your sulfate and salt levels are too high. Tall fescue has a moderate 8-10 dS salt tolerance so luckily you are below that, but you have too much salt for for fine fescues and bluegrasses to grow. Your sulfur level is at the upper limit for good growth however, so you need to be extra careful to avoid adding any sulfur or sulfates.

Not sure the source of the high levels, my guess is they were in the sod when they came? You should have your irrigation water tested for salt and sulfur, and minimize irrigation in the meantime. You need natural rain to help flush the salts out of the turf.

My recommendation would be to use a starter fertilizer (high P) one time, wait a month, and then you can switch to using regular fertilizers. You will want to stick to urea as your N source and avoid ammonium sulfate due to your high sulfates.

To lower pH while again avoiding any S, I think you should go with the citric acid option. pH will come down naturally with time from rain and fertilizer use.

Do not use FAS (sulfates). FYI P2O5 just refers to the phosphorus amount in the fertilizer, you can't buy or use P2O5 as a fertilizer anymore. It's a relic of how phosphorus used to be analyzed from ashes after burning plant tissue, the burning would covert it into the P2O5 form which was then directly used for fertilizer recommendations for hundreds of years now.


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## Virginiagal (Apr 24, 2017)

Starter fertilizer has nitrogen too and it's best to wait until early fall to fertilize with nitrogen. So hold off on fertilizing. Some organic fertilizers like Milorganite have a good amount of phosphorus,, so that's an option too. Phosphorus is the 2nd nutrient in NPK, and you can look at NPK numbers on bags where you buy lawn supplies to see what's available.

While your sulfur may be coming from the city water, it may be something else. While LeeB is advising to limit irrigation, I would instead water whenever it's needed. The irrigation water also helps to leach the excess salt and sulfur. I wonder if it would be helpful to collect rainwater in barrels and do some irrigation from that. You have a small yard, so it might be doable.


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## Virginiagal (Apr 24, 2017)

I looked up your climate. You have no rain until October. So rain barrels are useless. It also looks like you have no fall, just about the same temperatures year round. I looked up the extension office for Orange County. They are closed but working remotely. This looks 
like a good person there to contact:
James Michael Henry
[email protected]
He is a turf specialist. He should know appropriate times to fertilize. Probably knows about sodium and sulfur issues in the area.


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## Ridgerunner (May 16, 2017)

A little background information to help you in making decisions.
Your Salinity is at 4.8 dS/m. Generally anything below 2 is considered not detrimental to most plants and soil microbes. The lower the better for the plant/turf/microbes. High salt levels impede the plant/turf's ability to take up water, but the effect is plant specific. Some plants are more resistant (like Bermuda). The threshold for TTTF is about 3.9 and the higher the salinity, the greater the adverse affect. Fertilizers are salts. High sulfate levels are not toxic to plants, however high S levels can coincide with high salinity as the anion sulfate will combine with other elements creating salts. Remediating high salt content is best done by washing (leaching) the salts out of the root zone using irrigation or rainfall. 
Your SAR is 5.88. Although high sodium levels can interfere with nutrient uptake, the biggest issue occurs with soil structure. De-floculation occurs and water penetration is reduced. The higher the level, the more the de-floculation. When Values reach 13 (or 15% Na of Base Saturation), soil is considered "collapsed" and unsuitable for plant growth. 
It is recommended that a remediation plan be implemented when levels reach 6 (or 5% Na of Base Saturation). Standard remediation would involve Gypsum applications to replace the Na and then wash the Na out of the root Zone.
Your salinity and SAR levels are right at the cusp of the beginning to be detrimental. As the cure is to leach the salts and Na out, it's important that you make sure you aren't exacerbating your problems with the elements contained in your irrigation water. Hence, the recommendation that you access the suppliers analysis (most localities require testing and most utilities make them public, so no need to test it yourself).
Just in case that isn't enough to chew on: Salt content promotes floculation and counteracts the de-floculation effects of sodium.
Finally, this is new sod and sod farms commonly heavily fertilize. There is a good chance your test report may be skewed. Consequently, I wouldn't take any actions other than watering and fertilizing as needed this year and take another soil test next year and see where things are. BTW, your N levels are pretty high. Don't go overboard on N this year. Follow the min recs for TTTF for this Fall


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## LeeB (Jul 1, 2019)

Ridgerunner said:


> High sulfate levels are not toxic to plants, however high S levels can coincide with high salinity as the anion sulfate will combine with other elements creating salts.


I disagree with you a little there, once sulfate levels get to ~800-900 ppm (varies) they are toxic to plants. Anything in high enough levels will be toxic.

I would say no gypsum (sulfates) until the soil has been leached.


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## Ridgerunner (May 16, 2017)

LeeB said:


> Ridgerunner said:
> 
> 
> > High sulfate levels are not toxic to plants, however high S levels can coincide with high salinity as the anion sulfate will combine with other elements creating salts.
> ...


It's been a few years since I've researched the topic. I'd be interested in reading that study. Could you provide a link?


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## LeeB (Jul 1, 2019)

Ridgerunner said:


> It's been a few years since I've researched the topic. I'd be interested in reading that study. Could you provide a link?


https://www.paceturf.org/member/Documents/0410.pdf
https://www.paceturf.org/PTRI/Documents/Soil_tis/0309ref.pdf
https://www.ru.nl/publish/pages/546385/lamersetal1998est.pdf

Pace turf has looked at sulfur levels. Now I know sulfur and sulfate aren't the same, but I think you agree that most of the sulfur in the soil is going to end up in the sulfate form under normal aerobic conditions. Plants can handle a lot of sulfates, but at extreme levels you get a couple effects happening from what I see in the research. First is the potential to deplete other nutrients by exchange or precipitation, for example you could form iron(II) sulfide in the root zone and tie up all the iron. Phosphorus is normally bound to iron in the soil, so this causes phosphorus mobilization and eventual depletion. Eutrophication is another concern, especially if you have sulfate-reducing bacteria converting the sulfate into toxic sulfides. This can also make the root zone anaerobic which generally isn't good either.

I think the idea that sulfates aren't toxic came from a lack of seeing a toxic level in a lot of past work. It just takes a lot of sulfates, and perhaps the studies didn't go high enough with the concentrations, as seeing levels in the high hundreds or thousands of ppm is rare in natural soils. By comparison, some greenskeepers get concerned when they see S levels above 50 ppm.


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## Ridgerunner (May 16, 2017)

LeeB said:


> Ridgerunner said:
> 
> 
> > It's been a few years since I've researched the topic. I'd be interested in reading that study. Could you provide a link?
> ...


I believe you have misconstrued PACE's analysis and are confusing toxicity and salinity. 
"Excess levels of sulfur are rarely,* if ever, known to cause direct damage (i.e. toxic)* to turf."
Emphasis and parenthetical mine.
However, If you ever find a study that determines sulfate toxicity levels, please share it and Thanks for providing the links.


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