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If you're tilling raw leaves into the ground then yeah, I can see some nitrogen drift. I'm not sure how much but them microbes need to suck nitrogen from somewhere to digest the carbon in them leaves.
Why not compost the leaves first and then add to the soil?
I will use crunched leaves as a mulch to protect the surface. They'll take a long while to break down but the soil underneath doesn't dry out so much in this dry land. Haven't noticed any depletion of nitrogen but then I cover with a lot grass clippings and I'm not that observant.
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