Robyn Francis wrote:--
Mulches with a hard cellulose structure such as sawdust, wood chips,I'm having a hard time figuring out a mechanism for nitrogen to be drawn up more than a couple of millimeters, then across an interface, and into a fresh mulch layer.
eucalyptus leaves and pine needles have high N demands to break down. Some N
will be drawn from air but can also use up N from the top soil layer.
Fungal hyphae can transport nutrients, but it would be unusual to have a fungus with intact mycelial strands that cross the interface, from nicely decomposed earth into rough woody mulch.
I've always understood that the only place there is N lockup with mulch is right at the mulch/soil interface. The mulch doesn't have much nitrogen in it to start with (400 to 1 C/N or so), so what happens in the mulch itself can't be called locking up, just absence.
I've never noticed N-starvation in wood-mulched plants (and I use woody mulch almost exclusively. Quite the contrary--plants love it. But like I say, I'll listen to an alternative explanation.
Toby
http://patternliteracy.com
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