Soil Testing

[Sine Metu]

So I have been doing some research on soil testing this evening and I have a couple questions I have not been able to find an answer to.

How deep do you guys try to get a soil sample from for trees? Does it vary depending on the tree size? I stumbled on to AMS soil sample kits and based off of how their kits are set up I would be taking samples anywhere from 16" below surface to 48" below surface. I am in Virginia, and looked at the Virginia Tech cooperative lab and it is indicating 6" for trees and shrubs. Does this seem correct? If so, why then are soil sample kits designed to take samples as deep as 12' below the surface.

Basically I want to suggest a fertilizer for a client. They have a Black Tupelo, Blackgum that has some discoloration on the leaves and is not as thick/full as it should be. My gut is telling me a fertilizer will help, but before I suggest this, I want to conduct a soil test to first determine what the needs are for the tree. The tree is established, approximately 15'-20' tall with a 10'-15' spread on the canopy. Also I have never taken soil samples before, until now, never needed to fertilize or do anything that would require a sample.

Any light on the subject is greatly appreciated. Thank you

 

[ATH]

A) Good for you for taking soil samples rather then selling a "guess" as so many others do!
B) 80-90% of the tree's roots are in the top 18" of soil, so no need to go deeper than that. 6" sounds shallow. I am normally going down 12". I take off the top inch or so if it is in turf and use the rest.
C) I use a soil probe to take several plugs from all around the tree and them mix those together to come up with a sample.
D) What does the bottom of the tree look like? Is there a good root flare? Is there mulch around (but not piled against) the tree?

 

[Jason Douglas]

Im all for soil and tissue testing but that tree doesnt appear to have nutrient issues. Perhaps just a later season leave spot.

 

[Sine Metu]

A) Good for you for taking soil samples rather then selling a "guess" as so many others do!
B) 80-90% of the tree's roots are in the top 18" of soil, so no need to go deeper than that. 6" sounds shallow. I am normally going down 12". I take off the top inch or so if it is in turf and use the rest.
C) I use a soil probe to take several plugs from all around the tree and them mix those together to come up with a sample.
D) What does the bottom of the tree look like? Is there a good root flare? Is there mulch around (but not piled against) the tree?

Thank you, for the advice and the soil probe suggestion! Mulch ring around the tree, unfortunately I did not look/think to look at the root flare. The mulch is up to the bark, I remember that much just because of my landscaping background I always cringe when I see poor mulching jobs haha!

Im all for soil and tissue testing but that tree doesnt appear to have nutrient issues. Perhaps just a later season leave spot.

Gotchya... Couple questions off that, 1) is it something to be concerned about? 2) If so, I would have to get a tissue sample in order to diagnose that correct? or would the soil sample tell me that?

 

[ATH]

In the ideal world, they are done together.

I wouldn't take a tissue sample this late in the year...you want a newer leaf for good tissue sample. You can, however, get some information. If there are notable deficiencies found in the soil you will at least know those are there. If the soil looks good, but a tissue sample shows something deficient, you need to look at interactions a little closer and possibly other tree health issues.

 

[Sine Metu]

In the ideal world, they are done together.

I wouldn't take a tissue sample this late in the year...you want a newer leaf for good tissue sample. You can, however, get some information. If there are notable deficiencies found in the soil you will at least know those are there. If the soil looks good, but a tissue sample shows something deficient, you need to look at interactions a little closer and possibly other tree health issues.

Thank you.

 

[Jason Douglas]

And I wouldn't be too concerned about a fungal leaf spot unless significant and repeated defoliation occurs. Focus on leaf clean up in the fall to reduce inmoculum if possible.

 

[Sine Metu]

And I wouldn't be too concerned about a fungal leaf spot unless significant and repeated defoliation occurs. Focus on leaf clean up in the fall to reduce inmoculum if possible.

Okay I will keep an eye on it... granted it has been unusually dry and hot for us this time of year. Mostly upper 70's and low to mid 80's throughout September so I am sure that is a factor as well...only the last two weeks has the temperature started to drop and act like fall. Thank you both for your advice! I appreciate it.

 

[ropensaddle]

Thank you, for the advice and the soil probe suggestion! Mulch ring around the tree, unfortunately I did not look/think to look at the root flare. The mulch is up to the bark, I remember that much just because of my landscaping background I always cringe when I see poor mulching jobs haha!



Gotchya... Couple questions off that, 1) is it something to be concerned about? 2) If so, I would have to get a tissue sample in order to diagnose that correct? or would the soil sample tell me that?

The mulch up to the bark is poor mulching brother and can be causing girdling roots! Your quite correct; landscapers all make that mistake and it infuriates me to no end lol Start the mulch 6 to 12 inch from bark and spread a 2 inch layer to dripline of woodchips; over time fertilization will occur naturally giving both macro and micro nutrients almost ideal to plant health and encourage roots to spread out from the ball instead of circling!