On a related point, I’m no soil scientist, but I’ve always wondered why applications of P are so often proscribed as a prerequisite for establishing orchards because of “insufficient” quantities in the soil when actual deficiency symptoms in trees are so rare.
My sense is that P is an issue with annual plants in their first month or so, before they develop mycorrhizal relationships which provide adequate P in most soils for most plants once established.
Given how long it takes for science to sort out dietary and nutritional issues in human beings whose digestive processes and nutritional needs are easier to study, that it is about just a single species and that the investment in research is so much larger, one has to take the available information about plant nutrition with a grain of salt.
Most nutrients are grains of salt 
The salt dissolves in water. Nutrients as taken up by the plant are electrically charged ions.
Sufficient quanties of P not bound to the local soil can be important for root development in non-native plants.
Brassicas - a large annual crop group - do not develop significant mycorrhizal relationships.
Yes, so they say- the problem is finding any trees with actual P deficiency- in commercial fruit production it seems to be exceedingly rare. It’s not what’s in the soil, it’s what’s in the leaves. Also I believe the correlation of P to root development to be a debunked but often repeated myth.
Early studies came to these conclusions in artificial soils where it appears the less root growth was the result not of the lack of P but of the presence of N and that roots grow to reach both water and N. A plant needs put out less root if there is sufficient water and N nearby.
This is based on what I learned some 25 years ago, so if you have info that comes after that I’d love to see it.
I was referring to initial root development in the first month or so after planting. It is not something that would show up in leaf samples but rather in root vigor.
I agree though that P is over-rated as a fertilizer for many crops. The formula I developed for sustaining fruit trees is 16-8-24 … low in P by old-school standards.
Strongly concur with Alan. What very few people understand is that, if your soil is 7ppm P (very low), but biologically rich, when your plants finish that 7ppm, the myc. will produce another 7ppm from the unavailable P, which is there in quantities sufficient for millennia of agriculture. And the myc., when they form connections with roots, will also give your plants water, zinc, nitrogen and resistance to disease. Water of course is most important, and chemical fertilizers are proven to inhibit myc. activity. You really get to grow more with less work, less pollution and less money.
It is also true that brassicas and chenopodiums do not form myc. symbiosis. However, if farmers were to fertilize only these crops there would never be algae blooms. Growing cabbage in a spot, followed by 6 months of fallow, does destroy the myc. The solution to this is to never grow brassicas alone, at a small scale, but mixed with similar sized plants.
Always planting a new tree with myc. is a great idea, keep in mind that most fruit trees are endo-myc., but most forest trees are ecto-myc. I have started growing my own myc., using a method developed by the Rodale Institute (I use it on new trees and shrubs, allium, solanaceae, and cucurbita). Blueberries have their own class.
I like myc!
After dozens of spelling errors, I had to do something about it.
Any proof of this? I thought the problem was overall plant vigor in the case of vegetables unable to extract P from cold soil. I have read that an initial setting out of vegetable starts can be stunted by cool soil because biological processes don’t release much available P then and they have yet to establish mic relationships (having been grown in sterile potting mix).
I’ve never heard of a problem with trees as they run on stored nutrients immediately after transplant anyway, so this would be news to me.
Hence the advice to also add myc. to the pot, and hold the fertilizer, when you start tomatoes. I figure someone like Alan, or any farmer market guy, would profit from having his own stash of myc. to be added in every pot and every tree hole.
I just use my compost from a pile under trees and mix with last round of potting soil. I don’t purchase fungus that I personally don’t eat directly.
I was referring to this comment, not vegetables:
Yes, is there any evidence of this?
If I still had the publications from Cal-Poly SLO I’d provide them.
Thanks, that would be appreciated.
had … meaning I don’t.
Here is a broad discussion of research on increasing root growth of transplanted trees. P is not even mentioned and it is N that has successfully stimulated root growth in several studies but limited root growth in a couple of others.
I’m guessing the lack of info on P is because it has been dismissed as a root stimulator by researchers, but when I have time I will look for more.
The thing in this paper that surprised me is that recent research has shown that top reduction of transplanted trees can increase survival which contradicts rather extensive research by Carl Whitcomb back in the '70’s though 90’s.
Alan, I know that P as a fertilizer is a hot (
) topic for you. However, in this thread I was hoping to communicate with others about the topics in the original article “How phosphorus flows through an environment over many decades”.