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nitrogen tie up can be good can't it?

Posted by Jon_dear 4/5 (My Page) on
Tue, Dec 13, 11 at 15:58

Let's say you want to turn you mulch into a soil amendment by turning it under in the fall. Let's say it is old bark. You plant a legume that has been inoculated. That legume will have to work for its nitrogen because the micro herd is using the nitrogen to try and eat the bark (or sawdust or wood chips). The legume grows and produces noduals. Fast forward to spring.
The mulch turned amendment is breaking down well. The legume is turned under. The sun warms the soil. The nitrogen formed on the roots of the legume, as well as the green matter, works the mulch turned amendment more toward humus. Nitrogen is then released back to your soil for your plants to utilize.
Can it really be that easy? or should I start writing fiction?


Follow-Up Postings:

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RE: nitrogen tie up can be good can't it?

It's actually easier. Legumes obtain nitrogen from the air, not from the soil.

Here is a link that might be useful: wikipedia


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RE: nitrogen tie up can be good can't it?

It can be good to tie up nitrogen - that is in fact the reason for raising cover crops in some cases. If the nitrogen is "contained" during a period when you are not growing crops - stored in a cover crop over winter, for instance - it can be "released" in spring, as you say, for the nourishment of later plantings. But the method in these two cases is different. With legumes, nitrogen is essentially stored in the nodules while the plant is alive, and becomes available when the symbiotic process stops. In the case of your tilled-in mulch, the soil bacteria will "tie-up" the nitrogen until they are unable to utilize it any more, but likely not at a degree that is statistically significant. The goal is to maintain any nitrogen in the soil, and to reduce that lost as a gas.

Here is a link that might be useful: Ramial wood


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RE: nitrogen tie up can be good can't it?

It's actually easier. Legumes obtain nitrogen from the air, not from the soil.

That's the common belief, but it's only partly true. In a "good" year (e.g. good growing conditions, adequate moisture, etc.) legumes can get a majority, but not all, of their N from the air. In a not-so-good year, there will be a significant shortfall that will have to be made-up by other sources of N, whether that means N released from soil organic matter or N fertilizer supplemented by the grower. I'm not sure of the figures, and I would imagine it depends on which legumes you're growing, but I think a "good" year might mean 60-80% of N from nodulation and a bad year its well under 50%.


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RE: nitrogen tie up can be good can't it?

  • Posted by jolj 7b/8a-S.C.,USA (My Page) on
    Fri, Dec 16, 11 at 21:36

I know an older gardener(about 75-80 years)who is always proving the books & studies wrong.
He used round-up to keep weeds out of his corn for 4 years & the garden plot is still vegetables every year.
He does not mulch the corn & he puts down a little 10-10-10 around his pea. His pea is one he got from his Granfather, it is a type of black eyed southern pea.
He put green saw dust in his garden & around his blueberries with no nitrogen tie up that I could see.
He pots up grape vine & fig trees in leaf mold & garden soil.
Has the best looking plant I have seen anywhere.
When I point out that the PHD studies & book say he can not do what he is doing he laughs & said no more about it.


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RE: nitrogen tie up can be good can't it?

jolj, a lot of people do things all the time that contribute to the destruction of our earth. In the short term what they do may appear to work, but long term they are making life difficult for their grandchildren by polluting the air and water we need to survive.


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RE: nitrogen tie up can be good can't it?

My understanding is that cultivated annual legumes need sufficient N to be present to start with to experience good growth. Then the rhizobia can collect atmospheric N and sequester it, where it will be in the ground to enhance the growth of following crop. That is why legumes are often called "nitrogen-nuetral", they leave the ground with about as much N as they found. So if you plant a heavy-cropping legume like peas or beans in a soil low in N, then the yield will be quite poor, and the plants will leave little there. It is a different situation with say something like clover that is not getting grazed.

Still, using legumes to produce food for humans is like magic, you can pull out a nutritious crop and leave the ground as good as you found it or better.


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