permaculture

[Toby Hemenway <hemenway@jeffnet.org>]

> I am interested to know your opinions on tree and plant legumes in terms of
> when they release N.

I figured someone else would grab this; I'm kinda busy so I'll do it from memory rather than unearthing the citations. Radio-isotope (N) studies show that with tree and shrub legumes, very little N makes it into the soil (out of the nodules) until coppicing or cutting. A small percentage enters via leaf litter without coppicing within the first 6 months of labelling, but not much (enough to make a difference? Dunno). But after coppicing, the roots and nodules die back, and there's a very large flush of N into the soil. Seems to me there are data on alfalfa in Nyle Brady's "Nature and Properties of Soils" showing the same thing: at harvest, the roots pump N into soil, but not too much before harvest.

Toby
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