Removing sod when planting trees?

Yes the big fruit growers do learn a lot by watching other successful growers. It’s not all science. But the best growers like being on the research boards where they can learn from everyone.

And they tend to take all advice with a grain of salt, I think.

I agree completely. I enjoyed his book and read it several times, but I would not use it as a guide for commercial apple production. Fortunately, a lot of good production information is available from many state university systems. I just spent a long time evaluating several years of data of insecticide trials done by NC State. The results were unexpected. The insect counts in some cases were lower for the control blocks that were not sprayed and in some cases there was no significant statistical difference in the performance of the various insecticides that were tested. Fortunately, I was able to email the entomologist that did the trials and ask for his suggestions. Sometimes its difficult to draw conclusions when the data does not support it.

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Univ. of California research project that was designed by (then Ok. St.?) Carl Witcomb demonstrated that grass can inhibit new tree establishment if allowed within 18" of the trunk. [Actually his Ph.D. thesis was on this topic] Grasses apparently have an allelopathic ability within this proximity. So I assume it is a 3’ diameter zone recommended grass free.
[This comes from a lecture by Pam Bone, U of Calif. MG program: Planting and Care of Landscape Trees Part I and II where photographs of this research are shown. But danged if I can find a citeable publication of the results.]
This link provides an alternative to digging up the sod and that is heavy mulching the area (I would not use grass) to prevent grass growth. One must conclude that the allelopathic property must not be released from distressed or dying grass for this to work. Remember to keep mulch at least a couple of inches away from the trunk to prevent crown rots.

There are also a number of reasons why grass and trees do not co-exist well:
O'Dell Engineering - Land Connections - Trees vs. Turf Grasses - Modesto Landscape Architecture (unreferenced)

There is a ACTA Horta pub. that found of the grasses tested as ground cover only one was beneficial to tree growth (actually 3rd best of all the ground covers tested): St. Augustine. It does not like full sun and is typically found in dappled shade (from a tree), partial or to an extent full shade (it doesn’t do to well in full shade either). So it may be adapted to support trees.

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With regard to mycorrhiza, every soil is going to have native compatible AM and EcM fungal spores present. Even in low amounts (such as the arid southwestern soils of the USA) these adapted natives are likely to out compete even heavily inoculated commercial species unless from the same area. Microorganisms fight darned hard for the niches they already successfully occupy and are hard to dislocate.

If the soil has been disturbed and heavily amended the natives may be put at a disadvantage but only within the planting hole. I would not think this would lead to long term good things for the tree. Also keep in mind heavy presence of phosphate (as from fertilizer) inhibit these tree root-fungal interactions; who needs fungal parasites when you have all the phosphate you need?

I will look for a reference to an experiment demonstrating an infected plant signalling its resident mycelia that respond by secreting antibiotic for transport through the plant to ward off the infection. Really cool. [Still looking, but I ran across this cool one too on myelial signalling and adjacent plant response:]

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Check Whitcombs “Establishment and Maintenance…” he discusses the experiment which establishes the alleopathic traits of Kentucky blue grass to trees. The study was published in Agron. Jour, 65:126-129.

I just happen to have the book on my shelf.

Until your post, I never even considered the fact that only one grass species was tested- but that is a limitation of research. It is always very narrow and to be put to use one often makes presumptions.

You’re not seeing the whole picture. For one if all your trees have fungal relationships, they are interconnected. As you mention, some major advantages to that.As far as introduced species not competing well, here again i would disagree. We seem to have many invasive species of plants and animals, but not fungi? Our native species here are disappearing due to introductions. I would say that is totally wrong, unless you can produce studies that show your point? I highly doubt that new species would have much trouble establishing. And many of the studies I pointed to, collaborate that for sure. As all are from innoculant, and all did well for the most part. I guess one could disregard those studies, but that was the whole point of this discussion. Adding fungi, in all those studies was a very good thing. No leap of faith needed.

I notice the tree planting guide link I put here is out of date. Here it is again.