N-fixing facts and figures

Hi all,

I am designing and implementing a food / forest / garden. Given it is a place I only go once in a while, my main aim is to optimize the design to keep it as low maintenance as possible, including the fertilization steps. I will be using mostly trees and shrubs, while keeping native ground cover (more on that later). I know that some designers suggest the use of N-fixing trees and I even opened a thread here (https://permies.com/t/165799/fixing-plants-distance); in that post was Bill Mollison's explanation on the intensity of nitrogen around a legume tree (basically, nitrogen is made available only under the tree canopy).

My question is about conflicting criteria. On the one hand I need to harvest the fruits so for practical reasons it is unreasonable to plant anything under the tree canopy, which I keep with woodchips (for discouraging weed growth and all the other good things you are aware of); on the other hand I need a lot of nitrogen for heavy fruiters which can't apparently be supplied by the other nitrogen fixer trees.
How to solve this?

I also heard about mycorrhizal fungi moving the nutrients around. This would be great as I am in the middle of an established forest so there is probably a strong network of them anyway, and the native groundcover and bushes are all nitrogen fixers. But can I really expect mycorrhizal fungi to move the nitrogen around these distances (say, 30m)?

Besides these questions, I would gladly read more about the facts and figures beyond n-fixing: how much nitrogen can be made available per species, how far does it spread, etc. Scientific papers would be more than welcome. It's just more often than not the info I found is not scientific enough: I know the principles of planting a guild with dynamic accumulators and nitrogen fixers, but how does that translate into outputs of these plants and how does that compare with my plants needs?

Thanks

I cannot provide you with the science of nitrogen fixing but I can tell you what I am doing.

I am planning on planting Goumi and False Indigo between each of my fruit trees.  Both are nitrogen fixers.  Goumi is a sweet fruit and False Indigo is a good pollinator.

The Goumi ripens early in the season and I am hoping there is enough sun getting through the tree canopy to let them do well.  False Indigo Blooms early also but can handle partial shade and I am hoping Goumi is the same.

I am only growing naturally short trees. Pawpaw, Asian Persimmon, Asian Pear, Jujube and Kiwi Vine on a pergola. There are some Hybrid Astringent Persimmons that I will have to maintain at a shorter height. I have 10 feet between trees and 15 feet between rows so it will be a dense foilage.  
I am starting the trees as seedlings now and will propagate the Goumi next spring since I have several bushes going now.  My hope is they all get a good start at the sametime and can adapt to each other.

Hi Dennis I get your point, if you have success in your plants and harvests then you are probably fixing enough nitrogen and minerals. But again that is bypassing the original question. At this point there is so much data collected in studies, I am looking after some tables that would tell me how much nitrogen one plant needs and how much other plant fixes (beside what it needs for self consumption). Because there is the risk of too much or too little nitrogen fixation...