Evidence for nitrogen fixing trees

Do nitrogen fixing trees actually feed neighboring fruit and nut trees?

Lots of people out there advising planting them for that purpose. But, does it actually happen?

Do they only do it if they are pruned hard/coppiced?

If so, what is the mechanism which causes them to shed nitrogen when they are pruned? Does the pruning cause root nodules to explode in the ground?

I guess Ive seen many pages, videos and blogs claiming nitrogen fixing trees and shrubs should be added to the orchard, but very little if any actual evidence or explaination of HOW this happens, or how it works.

Id love if it were true, but it does makes sense a plant will only make nitrogen for itself, not all its neighbors.

Thanks
Josh

Joshua Stevens wrote:Do nitrogen fixing trees actually feed neighboring fruit and nut trees?

Lots of people out there advising planting them for that purpose. But, does it actually happen?

Do they only do it if they are pruned hard/coppiced?

If so, what is the mechanism which causes them to shed nitrogen when they are pruned? Does the pruning cause root nodules to explode in the ground?

I guess Ive seen many pages, videos and blogs claiming nitrogen fixing trees and shrubs should be added to the orchard, but very little if any actual evidence or explaination of HOW this happens, or how it works.

Id love if it were true, but it does makes sense a plant will only make nitrogen for itself, not all its neighbors.

Thanks
Josh

My understanding is that the nitrogen fixers fix nitrogen and keep it.  The leaf litter from those trees shares nitrogen, and as you said, pruning or coppicing releases nitrogen.  When the tree is coppiced, a lot of the feeder roots die off, leaving that nitrogen in the ground.

"when you coppice feeder roots die"

I thought the whole grand idea with coppicing was that the top gets cut but the roots keep growing larger and larger nearly forever, so you have super vigorous regrowth when the tree is cut in its cycles?? If coppicing kills the roots, would that not give a different result?

I think some of the roots die because there is suddenly not as big of a demand for nutrients. Maybe the tree can put its energy into regrowing new sprouts instead of maintaining roots that wont be fully used until the new branches are big enough to demand and draw up those nutrients. Not all of the roots die, just the ones supplying the cut branches.

Also, Paul thinks that nitrogen fixing plants share small amounts of nitrogen without  cutting the plant back. This may be due to tiny roots no longer being necessary when the local nutrients have been extracted. This is just my guess.