# SOIL TEST ANALYSIS



## Justice911 (Jun 1, 2019)

SOIL TEST QUESTION: Hello all. New member from Middletown, Delaware. I did a soil test on my lawn on March 16 and the photo depicts the results. As you can see my phosphorus is very low and the magnesium is excessive. What can anyone tell me about my soil . . . . good, bad?


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## g-man (Jun 15, 2017)

@Justice911 welcome to tlf. I moved your post to the soil folder.


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## g-man (Jun 15, 2017)

I don't recall how these index values work. Maybe someone else does.

You cant lower your mg. You can improve the ratio of ca to mg via adding gypsum. Gypsum will not change your pH. The pH is good at the current level.


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## Ridgerunner (May 16, 2017)

Indexes are a conversion of raw ppm values into a percentile-just a "grading system".
To convert UofDel FIV (Fertility Index Values) to the underlying ppm values:
Multiply Ca FIV by 10
Multiply Mg FIV by 1.31
Multiply K FIV by 1.82

UofDel has changed their scoring method for P. it used to be a 1:1 relationship, but they now grade more conservatively: Use the chart contained in this link to convert P FIV to ppm (or multiply P FIV by 0.8):
https://extension.udel.edu/factsheets/interpreting-soil-phosphorus-and-potassium-tests/


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## Ridgerunner (May 16, 2017)

"Excessive" in soil science is often a term of art. Sometimes it can be an indicator of amounts that could be detrimental (toxic) to plants, however, with regards to Ca and Mg it just refers to amounts that are above levels needed for plant use (those levels for Ca and Mg that are considered critical minimum values vary from 50 to 150 ppm for Mg and 350 to 750 ppm for Ca.) and has no relationship to toxicity.
It is commonly suggested that Ca:MG ratios fall between 3:1 and 10:1 for plant availability and soil tilth--but there is a lot of debate regarding Ca:Mg ratios and whether they have much of any effect on plant performance. 
To determine Ca;Mg ratios:
Calculat the meq of Ca and Mg. (the number of electrical charges - the number of CEC sites each holds in the soil.
ppm of Ca divided by 200
ppm of Mg divided by 120
Then divide meq of Ca by the meq of Mg.

For your soil, that Ca:Mg ratio is 2.7:1
780 ppm of Ca / 200 = 3.9 meq
173 ppm fo Mg / 120 = 1.44 meq
3.9 / 1.44 = 2.7 or a Ca:Mg ratio of 2.7:1

By reverse engineering the formulas, you can calculate the amount of Ca that would need to be added to adjust the ratio to a desired ratio. However if you are not experiencing issues (particularly tilth), if it isn't broken, don't try to fix it.


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