# Modified Morgan v. Mehlich 3



## KevC (Dec 27, 2018)

Earlier in January ahead of the (lasting) snow and deep freeze here in New Hampshire, I collected my first soil samples to get a game-plan and a baseline for the 2019 season. Both UNH and UMass are nearby, but have differing testing methods (Mehlich III v. Modified Morgan). Since I couldn't decide between the two, I opted to send a soil sample from the same "batch" to both.

below are the comparisons and results


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## g-man (Jun 15, 2017)

It was pretty cool to compare the two results. They looked similar, until I got to phosphorus. Something is not right.

CEC is in the middle. Nothing you need to do differently.
pH - 5.5. We need to improve this with lime.
Potassium - not deficient but you could improve it. Use SOP (0-0-50) if you could find it.
Since Mg looks good, then you should use calcitic lime to increase the pH.

This brings me to the one that had me scratching my head. Phosphorus. The UH report has it at a very high level. I haven't see values this high in P in a while. The UMass has it at an ok level. From what I know of the Morgan extraction, I don't think it affects P. Therefore I am assuming one is wrong. I know UMass is used a lot therefore I would lean on UH being incorrect.

Have you ever done a soil test in the past? Options: 1) give UH a call and share your UMass results. See if they could explain the difference. Or 2) collect new samples and send it again to them for testing. 3) send a sample to a 3rd lab.

@Ridgerunner thoughts?


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## Ridgerunner (May 16, 2017)

@g-man About the P? I think it's probably the M3 extracting more Al bound P. M3 results can be be 5-10 times higher.
Just my opinion.


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## Ridgerunner (May 16, 2017)

Just noticed that the Fe levels are indexed as high on the Modified Morgan results. I haven't seen enough Modified Morgan tests to judge how significantly "high" that is. So, in addition to Al, Fe also may be a factor in the P level differences between M3 and Modified Morgan. Not sure how much influence OM would have on the discrepancy at pH 5.5 considering the Modified Morgan would be expected to take that into account. I often wish I had a strong background in chemistry. Maybe one of the turf specialists here has the educational background to provide some greater insight. @osuturfman? @Greendoc ? @thegrassfactor ?


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## Ridgerunner (May 16, 2017)

@KevC What kind of P treatments, if any, have you done over the past couple of years?


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## g-man (Jun 15, 2017)

@BenC is another soil expert.


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## Ridgerunner (May 16, 2017)

:thumbup:


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## osuturfman (Aug 12, 2017)

First, let's talk about the sampling method:

1.) Did you pull many representative samples, combine that into one container, and then split it up for shipping to each lab? Or were these two distinct samples?

2.) What was your sampling depth? How consistent were you between the one sample? Or if you did two, how consistent were you between each sample?


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## desirous (Dec 15, 2017)

Ridgerunner said:


> Just noticed that the Fe levels are indexed as high on the Modified Morgan results.


@Ridgerunner, Fe is not really indexed as high. The numbers in the "optimum range" column have different meaning in the UMass reports, as stated on the form:

* Micronutrient deficiencies rarely occur in New England soils; therefore, an Optimum Range has never been defined. Values provided represent the normal range found in soils and are for reference only.


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## Ridgerunner (May 16, 2017)

@desirous Valid point. :thumbup: I knew that at one point, but had forgotten. My take was that as the MM test was supposedly developed for NE soils, that an amount of Fe significantly above what is "normal" might have an influence on the amount of P being extracted and account for some of the difference between MM and M3 results. Pure speculation on my part.


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## Greendoc (Mar 24, 2018)

Difference between Mehlich 3 and modified Morgan extractions is of course in the solutions. Mehlich 3 utilizes acidified and chelated Fluoride as the extractant. This aggressively extracts even tightly bound and in my opinion P that is not normally available to plants. Therefore overstating the amount of plant available P. Modified Morgan uses Sodium Acetate+Acetic Acid + EDTA. This is not nearly as aggressive as Mehlich 3. Mehlich 3 will solvate P bound to Aluminum, Iron, and Calcium. In real life, in soils, P does not readily become available to plants once bound to those elements. The high Iron readings are from how well EDTA chelates when in a neutral to acidic environment as provided by Sodium Acetate buffered by Acetic Acid.

I utilize soil tests to detect gross deficiencies or toxicity of elements. Growth rate, visual symptoms of deficiencies, or toxicities, confirm and then guide what I do next. Numbers on paper are a guide. However, I would probably lose clientele if I failed to green up a lawn because numbers on paper indicated that there was adequate nutrients according to one of these extraction tests and all it would take to get the grass greener was some soluble nutrients.


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## KevC (Dec 27, 2018)

g-man said:


> It was pretty cool to compare the two results. They looked similar, until I got to phosphorus. Something is not right.
> 
> CEC is in the middle. Nothing you need to do differently.
> pH - 5.5. We need to improve this with lime.
> ...


Thanks @g-man
This is my first test(s) - definitely thinking step one address pH level [with 50lb/1000 sq ft increments in spring/fall]
good heads up on calcitic lime (assuming dolomitic (sp?) lime would increase Mg levels)


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## KevC (Dec 27, 2018)

Ridgerunner said:


> @g-man About the P? I think it's probably the M3 extracting more Al bound P. M3 results can be be 5-10 times higher.
> Just my opinion.


Does this mean since the pH is so low that the Phosphorus can't be used by the turf - and may even impact testing/results due to being "locked up" (in a sense)


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## KevC (Dec 27, 2018)

Ridgerunner said:


> @KevC What kind of P treatments, if any, have you done over the past couple of years?


About 6 apps at bag rate of Milo/BayState over the last 18 months
Two or so big box store 10-10-10 spot Fert applications in flower beds around the front lawn that may have leached a bit
But likely the bio-solid program and the low pH level are the culprit on high Phos levels 
(Thinking UNH may be more accurate than UMass on Phos levels- but just my gut reaction)


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## KevC (Dec 27, 2018)

osuturfman said:


> First, let's talk about the sampling method:
> 
> 1.) Did you pull many representative samples, combine that into one container, and then split it up for shipping to each lab? Or were these two distinct samples?
> 
> 2.) What was your sampling depth? How consistent were you between the one sample? Or if you did two, how consistent were you between each sample?


Great question - and was thinking about describing in the original post - but kept it short and sweet
So I got a soil probe and really just wanted to tinker around with it - but waited a bit to long to get out to the yard and the top layer was partially frozen (pain in the neck) 
So I took about 12, 4" probe samples, pulled out turf and roots and let dry in one clean plastic bucket - then mixed and pulled a one cup sample to place into each clean plastic baggie and mailed off to respective university labs.
I tried to be consistent with 4" depth but .5" to 1" discrepancy possible to be honest


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## KevC (Dec 27, 2018)

desirous said:


> Ridgerunner said:
> 
> 
> > Just noticed that the Fe levels are indexed as high on the Modified Morgan results.
> ...


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## KevC (Dec 27, 2018)

desirous said:


> Ridgerunner said:
> 
> 
> > Just noticed that the Fe levels are indexed as high on the Modified Morgan results.
> ...


Also I did a few liquid iron apps last season - and wondering with the pH being out of balance the iron wasn't available and remains locked up


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## KevC (Dec 27, 2018)

Greendoc said:


> Difference between Mehlich 3 and modified Morgan extractions is of course in the solutions. Mehlich 3 utilizes acidified and chelated Fluoride as the extractant. This aggressively extracts even tightly bound and in my opinion P that is not normally available to plants. Therefore overstating the amount of plant available P. Modified Morgan uses Sodium Acetate+Acetic Acid + EDTA. This is not nearly as aggressive as Mehlich 3. Mehlich 3 will solvate P bound to Aluminum, Iron, and Calcium. In real life, in soils, P does not readily become available to plants once bound to those elements. The high Iron readings are from how well EDTA chelates when in a neutral to acidic environment as provided by Sodium Acetate buffered by Acetic Acid.
> 
> I utilize soil tests to detect gross deficiencies or toxicity of elements. Growth rate, visual symptoms of deficiencies, or toxicities, confirm and then guide what I do next. Numbers on paper are a guide. However, I would probably lose clientele if I failed to green up a lawn because numbers on paper indicated that there was adequate nutrients according to one of these extraction tests and all it would take to get the grass greener was some soluble nutrients.


I feel like I am playing checkers while you just called checkmate on me (ha) 
But totally get what you are saying - and yes trying to get a baseline on how to take my lawn to the next level, and we all got to start somewhere - and this community is completely invaluable to a home gamer such as myself 
So thanks to everyone


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## Greendoc (Mar 24, 2018)

Here's what I would do if that were my test. Use enough Calcium lime to raise pH to 6. Apply supplemental K, ideally Sulfate of Potash. Then apply enough N to achieve acceptable grass growth. You Iron is probably being competed with by the Manganese. I have heard of that happening on acidic soils. Correcting pH and then applying some Iron is a good plan.


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## KevC (Dec 27, 2018)

Thanks @Greendoc 
I'm going to scour the internet - but while I have your ear (and brain) is calcium lime widely available in box stores (as I'll need hundreds of lbs)
Not familiar with sulfate of potash (usually supplement K with a standard winterizer Fert) 
Will sulfur rates of 17% in some SOP label impact pH?


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## Greendoc (Mar 24, 2018)

It usually is available as garden lime. Do not use Dolomite lime because that is high Magnesium lime. The Sulfur in SOP does not affect pH at all. It is neutral in soils. I would look at fertilizer labels. I get the odd feeling that fertilizer manufacturers have been reading my rants about applying Potassium Chloride to turf. Many now use Potassium Sulfate as the Potassium source. You are ok to use a fertilizer that does that.


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## Ridgerunner (May 16, 2017)

KevC said:


> Ridgerunner said:
> 
> 
> > @g-man About the P? I think it's probably the M3 extracting more Al bound P. M3 results can be be 5-10 times higher.
> ...


Depends. Kinda yes, kinda No. Phosphorous is prone to bind with other elements in the soil, in high pH soils where Ca is in abundance, it mostly binds with Ca. In low pH soils where Iron and Aluminum are often in abundance, P binds with them. The purpose of soil testing is to attempt to measure how much of a nutrient will be available to the plant within a growing season period of time, That is, how much is in soil solution, the solution Pool (and immediately available to the plant-a very small amount) plus how much more is being held (bound "tied up" in chemical complexes or on exchange sites) within the soil where the bond "tie up" is weak enough *(labile)* to allow the nutrient to become available during that growth season time period, called the active pool. Some portion of nutrient is so tightly bound that it won't be available for years, called the fixed pool. The "trick" is to try and accurately measure the solution pool and the active pool and not the fixed pool. As @greendoc so well explained, the amount that is measured depends on the strength of the extract used, weak extracts report lower amounts, stronger extracts will report higher amounts. Debate rises whether weak extracts are measuring enough of the active pool and whether strong extracts measure too much of the fixed pool. Much depends on the type of soil. The usefulness of the results depend on how well they have been calibrated to plant response through multiple studies that have resulted in the development of "sufficiency ranges" specific to each test extract method. The span of these sufficiency ranges and how significant it is that a measured level falls into the upper or lower half of a range would likely be "fertile soil" for a greendoc rant, and understandably so.  
Does that help at all?


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## Ridgerunner (May 16, 2017)

A couple of good reads describing how dynamic and complex all of this can be. Expounding on/ following @Greendoc 's lead regarding MN and Fe:
http://edis.ifas.ufl.edu/ss555
Some really interesting explainations in the middle of this article:
https://archive.lib.msu.edu/tic/tgtre/article/2001sep6.pdf


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## osuturfman (Aug 12, 2017)

KevC said:


> osuturfman said:
> 
> 
> > First, let's talk about the sampling method:
> ...


Thanks for that info. I'm most concerned about the differences in P between your samples. As @Greendoc alluded to, we should and did see higher levels of P in the Mehlich III (M3) with a stronger extractant than the Modified Morgan (MM). The reason I asked about soil sampling depth and consistency is best illustrated in the slide below from Dr. Bill Kreuser at the University of Nebraska - Lincoln.



As you can see, P levels are very stratified within the soil. So when we see very high numbers there are three reasonable assumptions:


1.) You and/or the previous homeowner have seriously over applied. Except, your check on the MM doesn't bear out this conclusion.
2.) Your sampling depth was off and/or you scooped some soil that disproportionately represented the upper 1-2". This is possible but, would require a lot of weird variables to verify.
3.) Your M3 sample was contaminated with a fertilizer prill or remnants thereof. This is entirely possible and the most likely scenario to get levels that high.

If you're really up for it, pull another sample from roughly the same spots at a consistent 4" depth and send just that to UNH for M3 analysis to be sure. If not, no big deal.

The moral of the story is: sampling method and consistency from plug to plug and season to season are vital to having results you can plan around.


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## Greendoc (Mar 24, 2018)

One of the most useful exercises I went through was one in deliberate deficiencies. The instructor was in his 70s back in 1995. Old enough to have been around when sugarcane covered every inch of ground in my state. Corn was planted in peat moss and watered with a solution missing a different element for every sample. To this day, I know what a plant looks like when it is low in P, K, or the various micronutrients. I remember that excercise when looking at a lawn and seeing soil test results.


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## osuturfman (Aug 12, 2017)

Greendoc said:


> One of the most useful exercises I went through was one in deliberate deficiencies. The instructor was in his 70s back in 1995. Old enough to have been around when sugarcane covered every inch of ground in my state. Corn was planted in peat moss and watered with a solution missing a different element for every sample. To this day, I know what a plant looks like when it is low in P, K, or the various micronutrients. I remember that excercise when looking at a lawn and seeing soil test results.


Indeed. The unfortunate thing about turf is there's been so little work done, compared to agricultural crops, to calibrate sufficiency ranges with response and performance. In fact, many of the recommendations still used by some sources are merely correlated from agricultural crops and modified for turf. Most especially with N, P, and K.

The last 10-15 years have seen some big steps forward on this front, due in large part to the economics and environmental stewardship needs of the turf industry. I trust you'll see better recommendations in the coming years as this research continues. Until then, anyone who is serious about understanding how plant physiology is impact by soil chemistry should invest in Turfgrass Soil Fertility & Chemical Problems: Assessment and Management by Rieke, Waddington, and Carrow.

Google Books Preview
https://books.google.com/books/about/Turfgrass_Soil_Fertility_Chemical_Proble.html?id=u7Zqs-u91wcC&printsec=frontcover&source=kp_read_button#v=onepage&q&f=false

Amazon
https://www.amazon.com/Turfgrass-Soil-Fertility-Chemical-Problems/dp/1575041537


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## g-man (Jun 15, 2017)

@KevC I think my curiosity of understanding the difference in P made me forget the big picture. You don't have a P deficiency. You either are ok or have too much. Just don't apply any P this year unless you are doing a renovation.


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## KevC (Dec 27, 2018)

Ridgerunner said:


> KevC said:
> 
> 
> > Ridgerunner said:
> ...


Very helpful, insightful and interesting way to look at it with "active pool versus fixed pool"
And glad to be part of both a @greendoc and @Ridgerunner soil rant !


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## KevC (Dec 27, 2018)

g-man said:


> @KevC I think my curiosity of understanding the difference in P made me forget the big picture. You don't have a P deficiency. You either are ok or have too much. Just don't apply any P this year unless you are doing a renovation.


Yeah no worries - it's very eye opening to dive a layer deeper into the soil chemistry and easy to lose site of the Forrest in a rabbit hole😀
Guess I'll have to rethink my bio-solid plan - too bad as BayState (local Milo) just costs $1.75/1,000 sq ft


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## KevC (Dec 27, 2018)

osuturfman said:


> Greendoc said:
> 
> 
> > One of the most useful exercises I went through was one in deliberate deficiencies. The instructor was in his 70s back in 1995. Old enough to have been around when sugarcane covered every inch of ground in my state. Corn was planted in peat moss and watered with a solution missing a different element for every sample. To this day, I know what a plant looks like when it is low in P, K, or the various micronutrients. I remember that excercise when looking at a lawn and seeing soil test results.
> ...


I often listen to non-fiction audio books during my work commute - wonder how much would be lost (if audio versions are available) without visuals of diagrams and charts (if there is any) 
I took an agronomy class back in college and those texts were pretty visual from my recollection


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## KevC (Dec 27, 2018)

Greendoc said:


> It usually is available as garden lime. Do not use Dolomite lime because that is high Magnesium lime. The Sulfur in SOP does not affect pH at all. It is neutral in soils. I would look at fertilizer labels. I get the odd feeling that fertilizer manufacturers have been reading my rants about applying Potassium Chloride to turf. Many now use Potassium Sulfate as the Potassium source. You are ok to use a fertilizer that does that.


I am thinking of moving away from bio-solids due to the Phos levels - and just starting to look into other N sources. 
Should I be looking into Urea based or Ammonium sulfate sources for N. 
I like the idea of 46-0-0 synthetic N applied about 4 times (in NH) to get around 3-4lbs of N per 1000. 
Any advice appreciated @osuturfman @Ridgerunner @BenC


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## osuturfman (Aug 12, 2017)

Lots of options between quick release sources (urea or AMS) versus straight N slow release sources. Lots of experience shows you'll get about 4-5 weeks of response on quick release sources versus up to 12 weeks on the higher-end slow release.

Take a look at your Climate Appraisal on the Growth Potential Model.



And see below for more info on the GP Model.

https://www.paceturf.org/PTRI/Documents/0401ref01.pdf

Of particular importance in your chart is monthly N usage to try and maximize your desire to use urea and do so in shorter intervals. While this will require more apps, it's a smoother curve of response by the grass to N apps. Have a gander and feel free to inquire.


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## KevC (Dec 27, 2018)

thanks @osuturfman

very helpful table, hostorically my fertilizer mindset has always been so linear 4 or 5 seperate applications all at the same rate, but makes sense that the turf has differrent requirements at differernt times of the year
one thing that jumps out at me is the mid-summer fertilizer applications - particularly july/august - would likely be highly subjectable to current weather and irrigation patterns, often cool season grasses can go dormant around here late July early August


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## KevC (Dec 27, 2018)

what do you think of this label/product



Will certainly be an adjustment going from (20) 40lb bags of BayState/Milo to just (2) bags of this Lesco 28-0-3 for the season (would yield ~3.6 lbs of N per 1000 for the year).


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