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White on top of soil after wateringS  RSS feed

 
                          
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So my friend's house has their garden - a few beds in the back yard. They did a sunk/inset lasagna bed, but the top layer was dirt (no cardboard or hay) and planted a mixture of seeds and sprouted plants. Everything's coming up ok, and hte plants are doing fine with regular watering using two of those drip hoses (This kinda thing: http://www.google.com/products/catalog?q=drip+hoses&oe=utf-8&rls=org.mozilla:en-USfficial&client=firefox-a&um=1&ie=UTF-8&tbm=shop&cid=8221509451036786670&sa=X&ei=e5_tTdD-KcS1tgfu0rWrCQ&ved=0CHYQ8gIwAQ ).
Thing is, there's a very fine layer of white forming on top of the soil on the edges of where the water soaking extends to (like when you sweat on your shirt and you get salt, or what looks a lot like saltification of soil from pictures I've seen). It's being watered with municipal water here in Boulder, CO.
Now, I've heard that most saltification problems are due to irrigation. I'm not really clear on the dynamics of how much HOW water is evaporated (through plants vs off soil), or retained in the end affects saltification. For that matter I'm not even SURE the stuff is salt at all...
Does anyone have any advice/input on this?
 
John Polk
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Is your neighbor's water going through a water softener?  If so, it is probably picking up salt from there.
 
Brenda Groth
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may be they should get their water tested
 
                          
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No water softener.
Of course testing is an option.
Alternatives or ideas on how to just avoid/mitigate if it is salt/other problem?
 
Burra Maluca
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If it's salt from the irrigation water, what you need to do is reduce the amount of irrigation needed so that less salt is being added, and also reduce the amount of evaporation so that salt isn't being 'dumped' on the surface as the water disappears into the atmosphere. 

The drip hose combined with a nice layer of mulch, like straw, should take care of both those things.  I bet that with the mulch layer you won't need to run the irrigation anything like so often - just monitor the soil moisture levels and water as needed.
 
maikeru sumi-e
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Test soil pH. If alkaline, I have a strong suspicion it's excess calcium and other hard water minerals depositing on the surface of the soil. The Rockies have alkaline soils and hard water that can clog pipes and facets.
 
                          
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maikeru wrote:
Test soil pH. If alkaline, I have a strong suspicion it's excess calcium and other hard water minerals depositing on the surface of the soil. The Rockies have alkaline soils and hard water that can clog pipes and facets.


I'll look into this. Any ideas what kind of problem this may or may not be?

As for saltification, do you know?, does reducing direct soil-air evaporation only reduce SURFACE salt? or does it encourage the plants to take the salt in thus reducing long term saltification (other than the positive effect of not losing, and so not requiring, so much water).
 
Burra Maluca
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The way I understand it, if you reduce the evaporation, you reduce the need to add so much salty water.  Rain water is very very low in salts, but water from deeper down, which the water you are using to irrigate might be, will contain a higher percentage of salt.  If you apply it at the surface and most of it evaporates, then the salt will be dumped at the surface.  During heavy rains, that salt will wash down into the deeper levels again.  When there is more evaporation than precipitation going on, salt will build up on the surface.

I don't think it encourages plants to take more salt.  It's just not putting so much salty stuff on in the first place improves the balance between salt building up and salt washing down.  It's hard to explain in words, but if you keep putting on more than the soil will take then it will build up, so you want to make it so that what water you do use goes down into the soil, keeping the general salt flow downwards, not upwards.  And you want to keep *any* salty water to a bare minimum.  I can visualise it better than I can describe it - I think I need to set another homeschool animation project... 
 
maikeru sumi-e
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Supaiku wrote:
I'll look into this. Any ideas what kind of problem this may or may not be?


It's just the nature of the soils and water we get. Long ago many areas used to be at the bottoms of lakes, seas, or volcanic and have been uplifted and eroded, and the climate is both colder and hotter and drier, so the minerals have leached out from the Rockies but not yet leached away to the sea.

It may not be a problem at first but continual watering with the municipal water will cause the soil pH to keep rising until only alkaline-loving/tolerant plants can grow in the soil or you need to find a way to lower soil pH so plants don't suffer nutrient deficiencies. I live just a state over from you guys, along the Wasatch, and I've had people tell me that the hard water out there in Colorado is just as bad, if not worse, than the very hard water we get here.

As for saltification, do you know?, does reducing direct soil-air evaporation only reduce SURFACE salt? or does it encourage the plants to take the salt in thus reducing long term saltification (other than the positive effect of not losing, and so not requiring, so much water).


Reducing soil-air evaporation will help out a lot, but it depends on how many salts are dissolved in the municipal water and if there's any rainwater caught and used for watering/irrigation. Rainwater usually desalinates. Irrigation usually salts the ground. The important thing, as Burra Maluca mentioned, is to try not to add any more salt.

You can desalinate with a large flush of water, but this has the disadvantage of flushing out many soluble plant nutrients. Most grains, veggies, and fruits are not very salt tolerant, though some are better than others.

Soil salinization is one of the greatest threats the world faces today.
 
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