# MySoil Test Comparison



## CaffeinatedLawnCare (Apr 2, 2021)

Analysis of MySoil vs AgSource (NAPT/PAP participant) results:

For this comparison we will be disregarding 'ppm' given for each test, which are irrelevant because one is testing 'total amount' in the soil and the other is testing 'plant available only'. We will be looking mainly at the 'level' reported for each and use the ppm as a guide on how close those nutrients are to the proper level to help figure out a 'rating' in the cases where they are unrated.




```
Nutrient		MySoil Rating						AgSource Rating
pH			6.75 							7.4

Nitrogen		Low (1.17 ppm from 'Optimal')				Optimum
Phosphorus		High							High
Potassium		Low							Low
Sulfur			Low							Unrated (Low)
Calcium			High							Optimum (1.4% from 'High')
Magnesium		High							High
Sodium			Optimal							Optimum
Iron			High							Unrated (High)
Zinc			Low							Not rated (Low)
```
These weren't measured by AgSource:


```
Manganese		Optimal							Not Measured
Copper			Low							Not Measured
Boron			Low							Not Measured
```
Comparison:

Same 'rating' on 4/8, the other 4 are 'close enough' to be considered the same but either weren't given an explicit 'rating' or were only off by a small percentage. For most of the Micronutrients (and some Macros), the AgSource test didn't include them without paying extra, the 'extras' that I bought were Iron, Zinc, Sulfate, and Chloride (which MySoil didn't include).

Iron results were both High, Zinc results were both low, Sulfur results were both low, 3/3 are 'equivalent' as seen above.

In total 9/9 results above are 'equivalent' for both tests with nitrogen and calcium being the (slight) "outliers" and less than 2% difference between them. We would expect to see variation like this even within the same sample being tested and Nitrogen is known to vary widely in the soil with most tests omitting it completely. Neither of these differences is alarming or makes me doubt the credibility of either test.

Calcium to magnesium ratio:

```
MySoil				AgSource
2.95:1 				3.1:1
```
Again, almost identical results.

The biggest discrepancy between the two tests that would influence a soil amendment plan was the pH variance (~0.65pH, 6.75 vs. 7.4), pH has been shown to change up to 1 full point within a single season and is highly dependent on the salt concentration in the soil and the solution or water ratio (typically 1:1 or 1:2) they used to test the pH. Not only that but instrumentation differences and settling time can come into play, as well as the source of the distilled water used to test (if water was used). Judging from the table on the right in the image I shared showing nutrient availability (and the fact that MySoil measures 'plant available' nutrients) combined with the fact that the MySoil test is showing 'optimal' manganese availability, which is greatly reduced at higher pH (drops significantly when higher than 7 pH), and the 'high' iron availability, I would have to argue that the MySoil test is the more 'accurate' pH at 6.75. The MySoil result of 6.75 is also in line with my local cooperative soil test result from last year which came in at 6.7.

Recommendations:

I would have recommended a 2-0-1 or 3-0-1 ratio fertilizer based on either one of these results, which is exactly what AgSource recommends (1.4 lbs N and 0.5 lbs K, or 3-0-1). MySoils recommendations were either a 10-0-1 or 7-0-20, which were not what I would recommend. AgSource had a more accurate 'recommendation' for fertilizer with MySoil recommending products that didn't really correlate with their test results. Verdict here is to ignore the MySoil recommendations as far as fertilizer choice goes.

Conclusions:

Both MySoil and AgSource had nearly identical results in terms of nutrient 'levels'. MySoil arguably gave a more accurate measure of my pH. My findings here are that both tests were accurate and highly correlate to my local cooperative tests that I did last year. Both were more than adequate to base my fertilizer recommendations on, though I wouldn't rely on the generic recommendations that MySoil makes.


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## Virginiagal (Apr 24, 2017)

MySoil gives you a recommendation for ONE fertilizer application. AgSource gives you recommendations for a whole growing season.

MySoil does not do buffer pH and cannot give an accurate lime recommendation to bring pH up to a target. AgSource would do a buffer pH if your pH were below 6.5 and would give you the total amount of lime needed to bring up your pH to the target. Some soils are highly buffered and need lots of lime. Some soils are lightly buffered and need much less lime. The buffer pH is necessary to make a good lime recommendation.

AgSource is testing readily available nutrients, as is MySoil. All soil tests are testing what is extractable.

AgSource is not recommending a particular NPK ratio. They are recommending total pounds of nitrogen and potassium for the year. I think 1.4 pounds of nitrogen is low for KBG, that 3-4 pounds is better. In the notes it says for low maintenance do 1/2 pound of nitrogen in the spring, 1 pound in the fall, so I guess they're giving you a minimum amount for a generic lawn. If you had specified KBG, the recommendation should have been higher. The recommendation for 1/2 lb of potassium for the year seems reasonable. You didn't show the MySoil recommendation. It does seem strange that they would give a choice between a high potassium and a low potassium fertilizer. They recommend particular products that they sell, don't they? Again, one of my complaints is that a soil test that gives recommendations for only one application is not all that useful. You need to know how much phosphorus and potassium you need for the whole year. You might have been lower in potassium than you were. But would you need 1 lb or 2 lb or maybe even 3? AgSource would have told you. MySoil wouldn't.

AgSource gave you the cation exchange capacity(CEC); MySoil didn't. A CEC of 20 means your soil holds nutrients quite well. AgSource gave an organic matter percentage; MySoil didn't.


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## CaffeinatedLawnCare (Apr 2, 2021)

Thanks for the reply @Virginiagal, a lot to unpack here:

MySoil doesn't say anywhere that they recommend one fertilizer application with their 'recommendation'. I believe it says every 4-6 weeks during the growing season (way too much K for the 7-0-20, the 10-0-1 would be 'better' depending on how much N you plan to put down, but may or may not be enough K depending on the rate and how many times you apply it).



I agree that the buffer pH is not ever included with a MySoil test (and I'm not even sure it 'can' be calculated based on the ion exchange resins that they use and the way you deliver the sample to them already packaged in distilled water).

I may have been unclear when I said 'total amount' I meant 'total extractable amount', which is still going to be different than the ppm absorbed by the ion exchange resins. That's why I said we should ignore the ppm for the sake of the comparison and focus more on the 'ratings' that each were given since the ppm isn't going to be comparable between the two tests. But you are correct on your point here (depending on the pH and extractant used). This also makes it hard to determine an 'amount' to put down but can still be used as a guide of 'what' to put down.

AgSource is recommending 1.4lbs N and 0.5lbs K for the entire year. Which translates into a 3-0-1 ratio fertilizer applied for the entire year at the 0.5lb N in spring (0.16lb K) and 1lb N in fall (0.33lb K) for a total of ~1.4lb and ~0.5lb respectively. They don't directly recommend that ratio anywhere but that is what the ratio of N:K is ... 1.4:0.5 (essentially 1.5:0.5 or 3:1). You could achieve this with just urea/ams and SOP or two different fertilizers at rates that come out to a 3-0-1 ratio etc ... for our purposes we will just say a 3-0-1 ratio fertilizer at a rate that gives you the recommendations to make it easy. Either way, that isn't really the point of this post. MySoil is definitely just recommending products that they have a supplier for, but the recommendations themselves are not *great* at matching with the soil test results. That is why I think for all intents and purposes they should basically be ignored ... or at least heavily scrutinized beforehand (I don't like YM fertilizer anyway personally, large prill size, non-homogenous, poor quality ingredients). Either way ... I think I would end up going with a higher rate of N and K than either test suggest, probably closer to 4lbs of N and 1-2lbs of K.

Yes, each test had things the other did not, some of which I'll agree can be useful to know. Unfortunately for the AgSource test, each individual additional test was more $$$. One of the drawbacks of this test for sure ... but at least they are available if you're willing to spend the money. However, again, not really the point of this post ...

The main takeaway for me was that the general 'ratings' for each nutrient highly corresponded with each test. When one was high, the other was high and visa versa. There weren't any real 'anomalies' in any of the ratings. As a general guide of 'what' to put down, I feel like both tests were good. Though figuring out a rate to apply can be difficult with the MySoil test since the ppm doesn't mean a whole lot, I used it as a guide (it is either really far off, or really close to their 'optimal' rating to determine how much would be needed based on known yearly maximums, maybe more of an educated guess than anything). In the end though, I feel like that would be fine for most people with yearly tests to see how much additional you need/or don't need to put down.

Anyways thanks for your input let me know if you think of anything else or disagree with my thoughts here. Always glad to learn more and discuss .


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## Virginiagal (Apr 24, 2017)

Have you considered University of Wisconsin? Soil test for $15.
https://uwlab.soils.wisc.edu/soil-samples/lawn-garden/

Most people do soil tests to get fertilizer recommendations. And to see if they need lime and how much. MySoil's synthetic fertilizer recommendation would supply way too much potassium if it were repeated again and again. The organic one supplies hardly any potassium at all. It would be much better if they recommended a total of nitrogen, total of phosphorus, and total of potassium for the year. The 8 lb of 7-0-20 would supply about a half lb of nitrogen and 1.6 lb of potassium per 1000 sq ft. That's too much potassium in a single application. It does not inspire confidence.

Another thing AgSource has that MySoil doesn't is soluble salts. This is useful if there is any concern about saline soil (yours is fine).


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## Easyluck (Feb 5, 2019)

I'm curious how you sampled. Did you take multiple sample, mix them together, divide it into two samples and test them? Or did you take individual samples for each test?


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## Virginiagal (Apr 24, 2017)

It's Soil Savvy, not MySoil, that makes a recommendation for just one application. But MySoil's recommendations, at least on this test, are so off that they're not really useful.


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## CaffeinatedLawnCare (Apr 2, 2021)

@Virginiagal I specifically chose AgSource because it is a local lab that is part of the NAPT PAP program. I wanted to do a comparison with MySoil to discuss the results and why things would be different (or not). This was really more for fun than anything else (but I did need a soil test for this year after my reno last year anyway). I don't really need help analyzing the results for my own soil, just wanted to post this so everyone could look at the comparison and see the differences for themselves.

I agree that the recommendations from MySoil are all over the board, which is one of the things I pointed out in the original post. I don't like that they give very 'generic' recommendations it seems. If you're low on K they recommend the 7-0-20 even if you're only slightly deficient, which like you said doesn't inspire confidence in the recommendations at all.

But again was really more focused on the results that we could compare, which all seem to be in line with the AgSource results as far as what is high/optimum/low. That was the basic takeaway. Obviously we can't compare the other things that don't exist on one test or the other and the recommendations aren't needed. Judging from the results I plan to put down about 4lbs of N and 1-2lbs of K this year (which aren't the rates that EITHER test suggests - but at least AgSource was close).

@Easyluck I took multiple samples from an area in the front yard with a soil probe at a depth of 4-6" and mixed them together. I took a scoop of the mix and sent it to MySoil and the rest went to AgSource. Both tests are essentially on the 'same' sample.

Edit: Based on the above sampling method, I would expect the results to be very similar in terms of what nutrients were high/optimum/low. Which they were.


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## g-man (Jun 15, 2017)

pH variance (~0.65pH, 6.75 vs. 7.4). pH is a log scale, so a difference of 1.0 ph = 10 times different.

This soil only needs nitrogen. AMS would be my choice.


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## CaffeinatedLawnCare (Apr 2, 2021)

@g-man yes, that is the main difference that I saw as well. Though the MySoil test at 6.75 is more in line with the 6.7 result I got last year (I never applied any lime or other 'basic' material to the lawn, our water is 7.1pH). I would also expect to see lower available iron and lower available manganese at a 7.4 pH ... so honestly, in my opinion, the AgSource pH value is too high and the MySoil pH is correct.

Edit: I should mention that if you look back at my results from last year, which I just noticed I actually did test this area after fertilizing (whoops), it was the tree area that I was testing just so no one is confused, which was a 6.7 after fertilizing. So theoretically it could be closer to the 7.4 area which the 'non-tree area' section of the yard was at.

I applied quite a bit of potassium (SOP) last year to get it up to this level. My plan is to give it about 1lb this year and then hopefully none or a small maintenance app next year.

Just picked up a bag of AMS today as well so you read my mind there .


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## g-man (Jun 15, 2017)

I'm not sure what you mean by the iron. The extraction uses a different method than the pH method. The resin test used to have a statement that the pH can be wrong by 1pH. Without a third testing site, it is hard to pick the "right" one other than the one using proven methods.


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## CaffeinatedLawnCare (Apr 2, 2021)

@g-man I edited my previous post for more clarity, I was testing the area where my tree used to be (a relatively large section of my lawn) that came in at 6.7 last year using a third testing site (a local co-op). That is the same area I tested this year.

Though, looking back, that test was done in June after fertilization (which I now realize) so it wouldn't surprise me if it was higher now that there is less salt concentration in the soil and that area has undergone the same treatment as the rest of the lawn. However, this sample was just from that tree area, just so no one is confused if they looked back.

The 'iron' comment was that the ion exchange resins used in the MySoil test mimic plant extraction which would be affected by pH, so if my pH was high, I would expect to see decreased iron/manganese availability in the test. These two factors combined, the test showing high iron/optimal manganese + the previous test in this area from a third party showing 6.7, makes me think that the soil in that area is really closer to 6.7. However, the rest of the lawn was at 7.4 so it's possible that the 'tree spot' has acclimated somewhat and the material underneath broken down and now has a higher pH closer to the rest of the lawn? Seems plausible. It wouldn't really surprise me to have up to 1 pH difference, though in this case only ~0.65.

That was the main thing that seemed 'iffy' between the two tests. The rest of the nutrient analysis seems to match up quite well.


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## Ridgerunner (May 16, 2017)

I commend you on your efforts. Keep on researching and learning.


> @Easyluck I took multiple samples from an area in the front yard with a soil probe at a depth of 4-6" and mixed them together. I took a scoop of the mix and sent it to MySoil and the rest went to AgSource. Both tests are essentially on the 'same' sample.


Great. We are comparing apples to apples.



> Edit: Based on the above sampling method, I would expect the results to be very similar in terms of what nutrients were high/optimum/low. Which they were.


Not really.
pH. First there is little reason to believe MySoil results over a NAPT/PAP lab results.
6.75 vs 7.4. As g-man pointed out, a 6 and 1/2 times difference is significant.

Nitrogen. MySoil measured total N at 5.83 and Nitrate at 0.51 (no range given). with total Nitrogen rated low. Ag measure Nitrate alone at 9.6 which is close to the top or their recommended range. That's a significant difference.

Phosphorous: MySoil reports 11.35 which is .35 above their 5-11 range. That's 3% above the range. 3% isn't considered significant. Ag reports 57 which is 36 ppm above their 12-21 range. That's a whopping 170% above the recommended range.

Potassium. MySoil reports 20.85. That's 17 parts below recommended range. That's 44% below the minimum recommended range. Ag reports 159 ppm That's 1% below the recommended range.

Ag reports values that result in a 3:1 Ca to Mg ratio. Mysoils Ca and Mg values result in a 1.77:1 Ca to Mg ratio.

Those are all significant discrepancies. High/optimum/low don't have much significance. How High or low something is can be very significant. The big box stores sell a paper strip test that will pretty accurately tell you if the major nutrients are high/medium/low and you get four tests for $14. If that's your standard, the big box test is the better bang for your buck.


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## Virginiagal (Apr 24, 2017)

It looks like the way MySoil is coming up with a recommendation is this: "The soil is high in phosphorus and low in potassium so which of the fertilizers we're selling (or are being paid to promote) has no phosphorus and some potassium? We need an organic one and a synthetic one. Now what rate on these two fertilizers will supply about a half pound of nitrogen? That will be what we recommend every 4-6 weeks during the growing season."

Besides completely disregarding how much potassium is being supplied, this approach doesn't supply nitrogen appropriately. For most cool season grass a half pound every 4-6 weeks is okay in the spring, too much in the summer, and not enough in the fall. For a warm season grass like Bermuda it's not enough nitrogen. Does MySoil ask what kind of grass you're growing?

AgSource also has a problem in that regard. The crop listed is "Lawn." Fine fescue is fertilized entirely differently from KBG. Centipede is fertilized entirely differently from Bermuda. Nitrogen recommendations should be based on what type of grass you're growing. Did AgSource ask what kind of grass you're growing?


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## CaffeinatedLawnCare (Apr 2, 2021)

@Ridgerunner Thanks for the response, feel free to correct me if I'm wrong here but from what I understand of pH it can fluctuate pretty widely depending on several factors: what type of solution/volume rate you test the soil in (saturated paste, distilled water, salt solution, 1:1 ratio, 1:2 ratio), the salt concentration of the soil being tested (pH will drop after fertilizers have been applied), the instrumentation being used (how it was maintained, type of probe/litmus test, other environmental factors), the amount of time a solution is left to settle (pH of distilled water is known to vary widely depending on how long it is exposed to the air), etc.

Based on this, I wouldn't expect two labs to have identical pH values anyway. However, the MySoil result was closer to the previous result I had for this area which was 6.7. However, the rest of my soil was at 7.4 at the time of testing last year as I mentioned, so it's possible this area has come up since then, I also tested after fertilizer was applied, like I said in a previous post, so I wouldn't be surprised if it was actually higher this year as well. Some sources say a minor <=0.5 change in pH for the same sample suggests a high confidence result which, as you said, we are outside that range at 0.65. I think for our purposes we could conclude that we are most likely somewhere in between these two values. Again, I think it comes down to how much accuracy we really need to make good management decisions (whether to lime or not to lime and how much to apply - hard to determine from MySoil like Virginiagal suggested due to no buffer pH). In this particular case though, having a spread of 6.7-7.4, I would think no modification is needed.

As for the rest of your analysis here, there isn't really an objective/quantitative way to compare these ppm values, since as we've said in the past, there is no way to know how they determine the 'recommended range' or even how their recommended range compares to a different testing methods 'recommended range'. To say one has a 3% difference vs 170% difference is useless in this regard, since as mentioned earlier the scale may not be linear. 1ppm in the MySoil test could relate to 10-50ppm in the other test, we don't know. That's why I was avoiding making any direct comparisons to the ppm, which isn't apples to apples as you said earlier.

Same to the next statement.

Your math is wrong here ... Ag had a 3.1:1 ratio of Ca:Mg like you said but MySoil didn't have a 1.77:1 ratio as you're suggesting here. The results were 486.36 Ca, 165.05 Mg that is ~2.95:1 (486.36/165.05=2.9467 ... 165.05*2.9467=~486.36).

For the average homeowner I would think high/optimal/low (with some slight inference from the 'ppm range') would be 'good enough' to make a fertilizer decision for the year. I agree wholeheartedly that for this 'standard' of testing MySoil isn't entirely useful to someone like you or I who can read a little more in-depth into the results. I also would have to agree that for that kind accuracy it may be more cost effective to go with a home DIY test kit. I would say the only things going for it are the ease of use (homeowners are notoriously lazy) and the easy-to-read output.

As far as the testing method is concerned - ion exchange resins - I think they have a place in our toolbox based on some of the data that I have read on the subject showing that they can be a better indicator of plant tissue response to certain nutrients.

The comparison here was more to see the following:

1. Are the results trending in the same directions as an 'accredited' lab?
2. Could we make a recommendation based off these results?

I think for both 1 and 2 the answer is yes. Again, for the value, there are better options, but is it completely worthless junk that should be avoided? I wouldn't say that.


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## Ridgerunner (May 16, 2017)

You've collected a number of facts, but you misunderstand, misinterpret and misconstrue them.

It's apparent that your mind is made up, so I won't waste your time or mine confusing you with the applicable facts with the exception of the follow example:



> Your math is wrong here ... Ag had a 3.1:1 ratio of Ca:Mg like you said but MySoil didn't have a 1.77:1 ratio as you're suggesting here. The results were 486.36 Ca, 165.05 Mg that is ~2.95:1 (486.36/165.05=2.9467 ... 165.05*2.9467=~486.36).


Show me a reference that states that your method is how soil Ca:Mg ratios are calculated.


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## Virginiagal (Apr 24, 2017)

How can a test that merely says a nutrient is low be used to make a fertilizer recommendation? We need amounts. Traditional soil tests make recommendations for particular amounts needed of nutrients like phosphorus and potassium that can raise ppm by certain amounts, and they have data to back up what optimal amounts are and what amounts would do some good and what amounts won't. To just dump phosphorus and potassium on willy nilly (as MySoil was advising with potassium in your test) is irresponsible. Making fertilizer applications based on tests that give good fertilizer recommendations is the way to improve the crop (grass for us) without wasting resources and harming the environment.


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## Virginiagal (Apr 24, 2017)

Calcium to magnesium ratios are calculated by comparing millequivalents (mEq). Assuming the MySoil numbers are milligrams (we don't know what they are, they're just numbers on a page), here's how to convert mg to mEq:
https://onlinelibrary.wiley.com/doi/pdf/10.1002/9781119163411.app7

@Ridgerunner was making a good point in comparing how far out of the optimal range the results fell. For potassium, for example, AgSource found it was just slightly below optimal in its range. MySoil found it was about halfway between 0 and the minimal optimal number. So is potassium just slightly low or considerably low? He was comparing numbers on each test to its own ranges, not to the other test. We know what ppm is, which is what AgSource reports. We don't know what MySoil is measuring or how it came up with its optimal ranges.


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## CaffeinatedLawnCare (Apr 2, 2021)

Thanks for the responses @Ridgerunner and @Virginiagal, to Ridgerunner, I don't think your blanket statement of "my mind is made up" or that I'm misconstruing the data/facts is a constructive contribution here … but I appreciated your previous responses earlier and your questioning my math, that is how we learn. I was simply trying to respond to each of your statements individually because we are talking about multiple subjects (which my understanding of each varies) so you'll have to bear with me. I started my previous post with an invitation to correct me if I'm wrong (it won't be the first or last time that I'm wrong about something) but again, when talking about a broad subject that touches on multiple topics and sub topics it is hard to cover each thing individually while maintaining the overall conversation or thought process. I do appreciate you replying and sharing your knowledge so I wanted to get that out of the way.

There are several things here that I would like to know more about/discuss, so again, my mind isn't made up on a lot of this that I'm still learning about. The only thing my mind is made up on is that both tests reported similar overall "ratings" for each nutrient (the variances in ppm/percentages/ratios we will get to later and is definitely something that I haven't made up any kind of conclusion on). But since I'm on my phone at the moment it is hard for me to do all the calculations while on this small device ... I'll reply tomorrow with more of my thoughts and an actual look at the data and numbers based on what you and Virginiagal have said. One thing that I can definitely reply to now is in response to Virginiagal that MySoil states "all results are in ppm". The questionable thing to me is how that correlates to the ppm reported by AgSource so that's why, again to me, it is difficult to directly compare them, even if we are comparing the difference from each "range" within an individual test to the difference in "range" from the other test. Because the numbers don't correlate with each other even that comparison is useless since we don't know how much a change in one relates to a change in the other. By applying the 0.5 lbs of K from the AgSource test how many ppm will that increase the AgSource result and how much would we expect to see that same amount increase the MySoil result? Does it increase the AgSource result by 22 ppm and leave it directly in the middle of its optimum range? And if so do we expect that same amount to move the MySoil test 34.15 ppm leaving it directly in the middle of its optimum range? This doesn't seem like a question that is easily answered (or necessarily likely) my "assumption" would be that yes it would move both into their "optimum" ranges but how much the ppm of either test will change is questionable. I'm again assuming that the AgSource recommendation was meant to maintain or boost the potassium level up to within the listed range so I will try to contact them tomorrow for at least their portion of an answer, the rest would have to come from experiments like this to really find out.


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## Virginiagal (Apr 24, 2017)

I have an idea on why the pH may be different. Ag Source is testing a portion of soil sample itself. MySoil is testing a portion of the sample which has been nestled with a capsule that is exchanging hydrogen and hydroxide ions to collect cations and anions from the soil in the capsule to measure. It's not the same sample as it was before putting the capsule in. There have been chemical reactions going on before MySoil can test the pH.

Different extractants will come up with different ppm on the same soil. That's why you have to know which extractant was used to make sense of the results.


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## Ridgerunner (May 16, 2017)

One thing at a time.



> Show me a reference that states that your method is how soil Ca:Mg ratios are calculated.


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## bernstem (Jan 16, 2018)

Standard soil tests have been developed over decades of research. The reliability and validity have both been well studied and proven. If you want to embark on an analysis of testing methods, I would highly recommend that you familiarize youerself with the conceps of reliability and validity in testing. Delving into the two concepts is a good 2-4+ college lectures if not a full semester class, so I don't have the time or space to get into much detail on the two concepts, but I'll at least define them here.

Reliability is the degree to which a test will give the same results with the same inputs.

Validity is the degree to which a test is measuring somthing that is useful outside the test environment.

There are a number of different measures of reliability. Not all of them are really relevent to soil testing, but the concepts are useful. One type of reliability that is relevent to this discussion is paralell reliability. Paralell reliability is the degree to which two different tests will give the same result for the same sample.


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## CaffeinatedLawnCare (Apr 2, 2021)

@Virginiagal that is a good point about the pH as well and something to consider for sure, I would be curious to know how that affects the results. The only thing that makes me question it is the fact that I had the result from last year that I am comparing them to that seemed to be more in line with the MySoil test. But again, with the range I got back and considering the factors surrounding pH, I don't think any lime will be necessary. But for comparison sake, I'll definitely be curious to see what they look like next year and if the discrepancy still remains. I may even do a follow up later this year to see for myself how it is impacted. However, I will most likely wait until next year to repeat this process.

This is how I was viewing it when I did that calculation by comparing the ppm ratios:

"A Ca:Mg ratio of 5:1 is a statement of relative proportions of available calcium to magnesium. Two soils, one with 100 and 20 parts per million (ppm) of available calcium and magnesium and the other with 300 and 60 ppm available calcium and magnesium respectively, both have the same 5:1 ratio."

https://www.agvise.com/wp-content/uploads/2015/02/Nebraska-Cation-Ratios.pdf

In order to find the ratio as part of the CEC based on saturation percentages I would have to convert the ppm to meq/100g as Virginiagal suggested, which can be done like so:

https://ohioline.osu.edu/factsheet/anr-81

If I do that method and attempt to find the CEC and saturation % based on the MySoil test (and referencing the above method of converting the ppm into meq/100g) I would be unable to do the calculation because I am missing the buffer pH (which is needed to calculate the CEC). So, the only option would be to either do a buffer pH test on my soil or use the CEC reported on the AgSource test.

If I use the CEC value (20.7) on the AgSource test I can then calculate out the meq/100g equivalents from the MySoil ppm (though again, the ppm here doesn't mean a whole lot, which is why I didn't put too much stock into comparing the ppms):

486.36 / 200 = 2.4318

165.05 / 120 = 1.3754

20.85 / 390 = 0.05346

8.16 / 230 = 0.03548

From there I can then calculate the saturation % of each using the CEC:

(2.4318 / 20.7) x 100 = 11.75%

(1.3754 / 20.7) x 100 = 6.64%

(0.05346 / 20.7) x 100 = 0.26%

(0.03548 / 20.7) x 100 = 0.17%

So from this, I would only have an 11.75% saturation of calcium and a 6.64% saturation of magnesium (roughly 1.77:1) like you said. However, this is meaningless because we don't know how these ppm values relate to the actual soil (because of the extraction method, like Virginiagal mentioned) so how can we determine a soil saturation based on 'plant uptake' of nutrients that the MySoil test is supposed to simulate?

But, if I use the MySoil results to calculate the CEC (again I don't have a buffer pH to know if I need to add Acid Cations, so this is not very useful either) it comes out to ~3.896 meq/100g CEC instead of 20.7 which gives me:

(2.4318 / 3.896) x 100 = 62.42%

(1.3754 / 3.896) x 100 = 35.30%

(0.05346 / 3.896) x 100 = 1.37%

(0.03548 / 3.896) x 100 = 0.9%

Which again, also results in a ~1.77:1 ratio here, so based on this I would say I was wrong earlier or at least not comparing apples to apples. However, I still think these results are meaningless since we are comparing two sets of completely different values directly with no intermediary conversion from one to the other. That's why I said in the first place that doing a direct ppm to ppm comparison isn't going to be any use (I then proceeded to use the ppm to compare them in this case, which was a mistake on my part for sure).

Now if I take the 74.6% calcium and 24% magnesium saturation from the AgSource test and convert it back into ppm I get a result of 3,088.44 ppm and 596.16 ppm respectively. This comes out to a 5.18:1 ratio using the ppmpm comparison I did before. So either way those numbers definitely weren't correct. But again, this is how we learn and why I made this post.

However, none of this is relevant because we don't know how the numbers relate to the actual ppm value given by MySoil, so this comparison was flawed from the beginning and I shouldn't have used the ppm to directly compare with the other test like you also did in your first post, because we don't have a conversion factor to analyze them that way to even say if this analysis is right in terms of values given.

For example, if we can say that for every 10ppm change in the AgSource result MySoil will change 5ppm we could convert them into comparable numbers, however, it could be the case that there is no correlation in ppm values. As another example, if (because of the way they are absorbed) the MySoil test reports 486.36 ppm of calcium, but there is actually 3000+ppm and a different sample also reports 486.36 ppm (bear with me here) but is really closer to 1500 ppm (again because of the way it is extracted) there is not a good way to compare those directly (for instance by saying if one doubles, the other should double). In both cases there may be only 486 ppm of calcium that was absorbed by the resin test but widely different 'total extractable' amounts in the soil. In both cases the total calcium that was extracted would be considered 'optimal' because they are within range and as long as both percentages were within the AgSource range they would be reported as 'optimum' as well.

There are also other reasons why none of this is really important here, mostly because of the fact that many don't subscribe to the benefit of the theory on Ca:Mg ratios except in certain situations:

https://www.canr.msu.edu/news/soil_calcium_to_magnesium_ratios_should_not_concern_most_farmers#:~:text=Generally%2C%20calcium%20levels%20of%20less,greater%20than%2C%20calcium%20base%20saturation.

I think by putting too much stock into the ppm values given, and not looking holistically at the results, we're becoming too focused on 'what ifs' and less focused on the two questions that I mentioned in the previous post, I think in both cases the answer is still yes. However, I would love any further opinion and knowledge you can share and maybe some answers to the questions I've asked here.

Thanks again for taking the time to respond, I enjoy having these types of conversations and learning new things.

@bernstem Thanks for the reply, I have read quite a bit on the subject so far, but I agree there is tons of information to learn and dissect and really become familiar with. I think your post really sums up well what I was trying to get at with my initial post. From what I can tell here there is a high amount of parallelism between the two test results I got back here. Especially if we ignore the 'ppm' value for each and focus more on the ratings themselves.

I don't necessarily agree with not being able to recommend a fertilizer based solely on high/opt/low levels. I would think that (for most people) you could get 'close enough' with this basic information and a 'general' idea of how high/low you are within that range. If you combine this with a general knowledge of 'acceptable' rates to apply (for instance potassium that we've discussed a bit here being generally put down at rates between 0-6lbs/1 M) we could then infer that being low (but not excessively low, based on the results shown) I would be best off to apply between 1-3lbs for the year. If I combine that with the 'general' recommendation of 2-4lbs of N per year, I would be looking at something between a 1-0-1 (ish) and 4-0-1 ratio fertilizer. I think for most people this would do just fine, then when you re-test the following year you can determine 'how much' the fertilizer changed your result and adjust from there.

This strategy should result in a close approximation of your nutrient needs without wasting excessive amounts of fertilizer (that some recommendations may result in). Is it going to get you perfectly accurate results? No, but I think for the general public it would be more than adequate to guide a decision. If you're trying to measure your potassium needs down to the gram, probably not.


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## g-man (Jun 15, 2017)

After some blood work, your doctor says: Your cholesterol is high. You should buy this drug i sell.

But how high is it? Good or bad cholesterol? This is some special test that doesn't use units but the graph shows high.

How was my A1c in that blood work? We don't do that test.

Can I use something other product? How many milligrams per day?


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## Virginiagal (Apr 24, 2017)

Good reasons not to use MySoil:
1. No buffer test. People with acidic soil won't know how much lime they need.
2. No studies to establish what nutrient values, as extracted by the MySoil test, correspond to the levels needed for good growth.
3. Fertilizer recommendations are bizarre.
4. pH is perhaps not accurate.

I don't see the benefit you apparently see with this method. What I gather is that you are intrigued by the idea that it simulates what's available at the root. But all extractants measure what's available, not total nutrients. The nutrients that are bound up in various ways don't get counted. They aren't extracted with any extractants. What gets extracted in a traditional soil test is what's in the soil solution and what is on the cation sites. The nutrients in the soil solution and on the cation sites are available to the root. With a traditional soil test, you get back results you can compare with known levels. They have meaning. You get reasonable fertilizer recommendations and don't have to guess whether you need 1 lb or 3 lb of potassium per 1000 sq ft. The university tests are less expensive. Yet you keep promoting MySoil "for the general public." I don't get it.

Suggestion for something else you might find intriguing: mycorrhizae. Maybe you haven't read much about them, but they are fascinating. There is so much going on down in the soil.


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## Ridgerunner (May 16, 2017)

You don't need to know the total CEC or amount of acidity nor K or Na to determine the Ca;Mg ratio. Although the proportion (%) of Ca and Mg to total CEC will change, the mEq of Ca and Mg does not, nor does their ratio to one another. To determine Ca to Mg ratio all you need to know is their mEq.

If you accept that AgSource is a reliable (gold) standard and their measurements are accurate, then any discrepancy (larger than standard deviation-5%) between Ag's findings, in relative nutrient quantities (not differences in units of measurement but in relative quantities) and pH, and MySoil's findings should raise red flags.The reported values between tests should have a linear relationship-See @bernstem post. If you question the validity of Ag's testing, then no sense in continuing the discussion.

So far, everytime a discrepancy is pointed out, you discount it as a "useless" or unimportant measurement anyway. (that indicates to me a bias, that your mind is made up- and yes, my mind is made up as far as MySoil and SS and YM is concerned) It may be true that some of these measurements my have little practical value, but the differences between test raise concerns regarding the accuracy and consequently the usefulness of the MySoil report. You discount the differences between Ag reported nutrient values and their recommended ranges vs the differences between MySoil reported nutrient values and their recommended ranges as "useless. Yet now you proffer that by observing how low a nutrient level is below the recommended range, you can infer the amount of fertilizer needed.
In my opinion MySoil and the like are inappropriate, money wasting tests for home lawns, even if they were accurate and repeatable and I'm willing to factually defend this position. This isn't personal, but anytime someone promotes expensive gimmicks, I'm going to push back and hard.


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## CaffeinatedLawnCare (Apr 2, 2021)

@g-man I know what you're trying to say but it is sort of a bad example as those are actually two completely different tests (lipid panel and hemoglobin glycosylated, I actually, just recently, had these done lol) and there are things the AgSource test didn't include as well without paying for separate tests. Could we possibly pay MySoil to calculate and provide the CEC/OM%, etc.? Possibly ... never asked ... I know it isn't included in their 'standard' tests.

It also does include 'units' (ppm), what my point was is that we can't really compare a Bray-1 result to a MySoil result directly without knowing how to convert between the two and what response the two tests have to the same amount of applied fertilizer. To simply say "well this one is off by X amount compared to this one" doesn't seem to make any sense to me without knowing how they relate to each other. You can just say "oh they should have a 'linear' relationship", but they may not, we really won't know without testing/evidence of this relationship.

If I apply 0.5lb of K this year, how much will that move the needle on the AgSource test vs the MySoil test? All I have is speculation at this point and no real answers.

@Virginiagal All valid points (with the exception of maybe #2), I would have to say that #1 + #4 (both relating to pH) are something that I think is flawed with the MySoil test (in terms of not providing a buffer pH). I'm not sure if this was done as a result of how the soil sample is provided (since we only provide one sample and it is already in a solution of distilled water with a resin capsule) are they then not able to use that same sample to do a buffer test? I would definitely be curious on the answer to that. Maybe they simply don't provide it to avoid confusion and instead just use it to calculate lime amounts in their recommendation (if they are needed). Also a good question I think and a 'downside' for sure if you are expecting to see it.

The actual legitimacy of the pH measurement itself is definitely something I'll be looking at closely for any more comparisons in the future ... (Did I alter the result with my sampling technique? Is the MySoil result the same as the third party result again next time? Does perhaps the AgSource result match up in subsequent tests?) All things I'll be looking at for sure.

As far as the fertilizer recommendations go, I think we're all in agreement that they are strange to say the least ...

So after thinking about it a bit, I would say that 3 out of your 4 'good reasons' are slightly questionable ...

1. No buffer test, but they may still be calculating out the lime requirement when providing their recommendation.
2. Studies have been conducted by MySoil (the owner of the product testing their own product? Blasphemy) and they have established their own guidelines. However, there is evidence, in other research, of the correlations between plant response and ion exchange resin testing, so there is that. Here is just one example of such research:

"In conclusion, the results showed that the resin procedure better evaluated the increase in P availability due to liming, while Mehlich 1 and Bray 1 were not sensitive to the changes caused by variation of soil pH. Olsen indicated a decrease in available P, which was inconsistent with leaf P concentration."

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.9492&rep=rep1&type=pdf

4. We haven't established whether the pH is really accurate or not, though it was more in line with my previous test than AgSource. Or if it was something environmental (differences in the soil composite, my technique, etc.) that caused the differences. So I'm not advocating for either test being right or wrong but simply pointing out my results.

The one good reason I see from your list is that the fertilizer recommendations are bizarre in some cases. Though if you really aren't looking for them to provide the fertilizer choice it doesn't really matter, as long as you understand what you need to do and are able to infer from their test an applicable strategy.

To your next point, I'm not 'advocating', 'promoting', or even 'recommending' MySoil vs. another test. This was simply to show the results and talk about them in a constructive way rather than just say 'they are unreliable/unproven don't use them' and end the conversation there, because frankly, there are tons of people using these tests. I would like to be able to provide help to others who are using these tests by better understanding them and being able to (objectively) compare and explain the results/deficiencies/benefits. Which I think we've identified a few of each.

Again, when I say that they are probably 'good enough' for most people to make a determination, I'm not 'promoting' them to the general public, I'm saying that if someone decides that the MySoil test is worth it (for whatever reason) and they get one, there is still benefit (based on what I've seen). There are plenty of people out there today applying Milorganite on a regular basis that have extremely high P levels, if this test can identify that they have 'high' phosphorus and get them to switch fertilizer, that in itself is a good thing without even knowing the 'exact' amounts they should be putting down. That's all I'm getting at. I'm definitely not saying one is better than the other or that I would recommend MySoil over AgSource.

I know about mycorrhizae and yes there are multiple factors going on in the soil and with the plant (microbes, organic matter, soil type, grass type, even cultivar, etc.) that really any recommendation by anyone for any 'amount' of fertilizer to apply is going to be 'off' to some degree from what may be the best amount. I don't think that is extremely important to having a nice lawn as long as you aren't applying excessive amounts or not giving it enough ... which again, I think the MySoil test does an OK job of providing the basis for a 'decent' recommendation which at the end of the day is what we're using a soil test for. And I feel like I need to keep saying this, but this is in no way me saying 'MySoil is what everyone should use', I'm just objectively trying to look at it for something to do in the off-season while I wait for my first mow :lol:.


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## Virginiagal (Apr 24, 2017)

I will grant you that ion exchange could show promise as a possible future method for soil testing. It seems to collect cations and anions from any type of soil and right now extractants work well in some types of soil and not so well in other types. That's why calcareous soil should be analyzed with elevated pH ammonium acetate instead of other extractants. It also seems to be easier for labs to do an analysis because they don't have to use one substance to test for this and another to test for that

The capsule is collecting cations and anions by exchange and then an eluate (I learned a new word) is used to disconnect them from the capsule for analysis by chromatography. The soil sent with the capsule isn't being analyzed except for pH.

If MySoil and Soil Savvy want to gain some respect, they should show the field studies done, if any, that show plant response at certain levels of nutrients analyzed their way. They should show how they came up with their range of optimal levels. They're not sharing that information. Instead they are running an analysis and making slap dash recommendations which could even be harmful. No way would I recommend anyone use them, least of all the general public.

They could easily include a separate bag for the soil to be tested for pH and it wouldn't get contaminated by the ion exchange going on. They could easily test for buffer pH too. They're not. They could possibly make specific, reasonable P and K recommendations for a whole season. They're not. They're making a recommendation for a single application of a particular product based on whether P and K are low or high (Soil Savvy) or a repeated application, without any nuance, of a product that is either high or low in P or K (MySoil). The rates are based on the nitrogen in the product being promoted. The P and K recommended can be all over the place. That is just plain irresponsible.

Are there universities doing studies on ion exchange for soil testing? What are they finding? Are there reasons they're not doing studies? Do they know something about limitations on the process that make it not as useful for soil testing? Could there be time issues (how long the capsule has to collect cations and anions) or temperature issues that impede accuracy?


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## bernstem (Jan 16, 2018)

https://cdnsciencepub.com/doi/pdf/10.4141/S00-091


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