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Author Topic: How does sodium nitrate make soil alkaline?  (Read 6339 times)

Offline sasha44

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How does sodium nitrate make soil alkaline?
« on: 29/06/2011 20:51:13 »
Our lecturer told us that when Sodium Nitrate is added as a strait fertilizer the soil becomes alkaline with time. How does this happen? She didn't give any explanation and asked us to find out. So far I had no luck with it. The possible answer I've found is that Nitrate turns to nitrite , then nitrite reacts with water to give HNO2 and H+. But I'm not sure whether thats entirely right. Help!  ???


 

Offline Bored chemist

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How does sodium nitrate make soil alkaline?
« Reply #1 on: 29/06/2011 21:24:17 »
Why do people add NaNO3 to the soil?
Once you think about that you might realise what's going on.
 

Offline sasha44

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How does sodium nitrate make soil alkaline?
« Reply #2 on: 29/06/2011 21:42:13 »
Well they add it to add N to soil as NO3- so that plants can absorb it immediately. Lets see
when you add water NaNO3 fully dissociate as Na+ and NO3- and NO3- is absorbed and removed from the system. Leaving Na+
And whats left in the medium is Na+ H2O and H+ and OH- (from the partial dissociation of water) and rest of NO3-
H2O reversible arrowOH- + H+
Now how does the system make the extra positive charges of Na+ neutral?  :o

am I getting anywhere near? I have no idea on this one
« Last Edit: 29/06/2011 22:27:56 by sasha44 »
 

Offline Bored chemist

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How does sodium nitrate make soil alkaline?
« Reply #3 on: 30/06/2011 07:00:03 »
You are getting there. The magic ingredient is that plants swap nitrate for carbonate (which they make from CO2)
 

Offline sasha44

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How does sodium nitrate make soil alkaline?
« Reply #4 on: 30/06/2011 07:58:31 »
Ahaa  ;D Now I get it ! CO32-(aq) + H2O(l) reversible arrow HCO3-(aq) + OH-(aq)
which makes the medium alkaline

Thanks a lot for helping out!!  :)
 

Offline Bill.D.Katt.

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How does sodium nitrate make soil alkaline?
« Reply #5 on: 01/07/2011 05:36:24 »
Slightly off topic, but I was wondering, wouldn't using NaNO3 instead of KNO3 be very similar to salting the earth? And as a fertilizer wouldn't it do more harm than good?

-[I'm assuming the above spam will be deleted]-
 

Offline damocles

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How does sodium nitrate make soil alkaline?
« Reply #6 on: 03/07/2011 03:23:27 »
Umm...

Not sure, but I think that all of these inorganic reactions are fairly fast reactions, and that they do not really demonstrate a lowering of soil acidity, because hydrogen ions (acid) seem to be a by-product of each of them.

I think that a microbiological process of some sort is a more likely explanation of a process that happens "with time". I know that there are some microbes that can use nitrate or nitrite as an oxidant when no atmospheric oxygen is available. Is it possible that ammonia, which is alkaline, might be produced as a by-product of this sort of thing?
 

Offline Bored chemist

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How does sodium nitrate make soil alkaline?
« Reply #7 on: 03/07/2011 10:01:31 »
Bill,
for a lot of plants potassium nitrate is very much preferred as a fertiliser for just the reason you give. Though I understand that the sodium salt is used to fertilise sugar beet. It's a descendent of sea side plants. It's not troubled by the sodium and the sodium keeps the weeds down.

Damocles,
plants grow slowly.
They take up nitrogen slowly.
The change in pH is slow.
In essence, if you take the nitrogen away (to plants or bacteria) the sodium is still left behind. Unless there's some source of a counter ion for the sodium, it will be present as the hydroxide. That's going to make things alkaline
 

Offline damocles

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How does sodium nitrate make soil alkaline?
« Reply #8 on: 03/07/2011 10:17:36 »
From Bored chemist
Quote
Damocles,
plants grow slowly.
They take up nitrogen slowly.
The change in pH is slow.
In essence, if you take the nitrogen away (to plants or bacteria) the sodium is still left behind. Unless there's some source of a counter ion for the sodium, it will be present as the hydroxide. That's going to make things alkaline

Yes that is fair enough comment ! The only small problem that I see with it is that I am pretty sure plants cannot directly use nitrate -- they want their nitrogen in -3 oxidation state, like ammonia or cyanide or urea.
 

Offline Bored chemist

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How does sodium nitrate make soil alkaline?
« Reply #9 on: 03/07/2011 14:08:11 »
It doesn't matter much. Some plants can use nitrate directly, others rely on bacteria to convert it to ammonium but once it's taken up by the plant there's still the sodium left behind and the soil becomes alkaline.
(some plants can collect so much nitrate that they become marginally toxic)
 

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How does sodium nitrate make soil alkaline?
« Reply #9 on: 03/07/2011 14:08:11 »

 

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