Register to reply

Salting the earth

by noblerare
Tags: earth, salting
Share this thread:
noblerare
#1
Jul6-09, 07:02 PM
P: 44
I recently read that after a war was fought, the victors would salt the land of their defeated opponents to prevent anything from growing.

I understand that the salt would suck out the water from the soil that would prevent the plants from getting enough nutrients and water. However, how long does this salt on the ground last for? I would think that past armies would salt the land because they wanted to completely decimate their opponent, meaning that the ground would never grow anything ever again. This seems unlikely though. Wouldn't the soil, after years or decades, still be able to bear crops? If the salt on the ground really does that much damage, does that mean that there are patches of land around Italy (i.e. Rome vs Carthage) or Europe in general that cannot bear any crops?

Please enlighten me on this issue. Thank you
Phys.Org News Partner Science news on Phys.org
World's largest solar boat on Greek prehistoric mission
Google searches hold key to future market crashes
Mineral magic? Common mineral capable of making and breaking bonds
mgb_phys
#2
Jul6-09, 07:20 PM
Sci Advisor
HW Helper
P: 8,954
The salt doesn't simply absorb water it is absorbed by and kills many plants. The salt remains until it is washed or blown away, that depends on how much salt you add and how stable the soil is.
It's also problem where you drain seawater from an area to plant like the polders in Holland.
CRGreathouse
#3
Jul6-09, 09:28 PM
Sci Advisor
HW Helper
P: 3,684
Quote Quote by noblerare View Post
I recently read that after a war was fought, the victors would salt the land of their defeated opponents to prevent anything from growing.
Rome is supposed to have done that to Carthage after the third Punic war, but I don't think they actually did.

Proton Soup
#4
Jul6-09, 09:51 PM
P: 1,070
Salting the earth

Quote Quote by CRGreathouse View Post
Rome is supposed to have done that to Carthage after the third Punic war, but I don't think they actually did.
i never thought about it before, but it seems like it would take a lot of salt. or seawater.
noblerare
#5
Jul6-09, 11:13 PM
P: 44
So, if the salt is placed on the earth, it will remain there until it is blown or washed away? So does that mean that theoretically, if armies salted the earth of the defeated and used a respectful amount of salt, nothing could possibly grow on that soil EVER AGAIN?

Would rain water or river water wash away the salt? For example, if the land around China's Yellow River was salted, would it not be very effective because the Yellow River floods so often and washes away the salt?
mgb_phys
#6
Jul6-09, 11:25 PM
Sci Advisor
HW Helper
P: 8,954
Quote Quote by noblerare View Post
So, if the salt is placed on the earth, it will remain there until it is blown or washed away? So does that mean that theoretically, if armies salted the earth of the defeated and used a respectful amount of salt, nothing could possibly grow on that soil EVER AGAIN?
if they used enough salt that salt tollerant plants wouldn't grow then yes. Until the salt was washed or blown away

Would rain water or river water wash away the salt?
yes - assuming the water drained to somewhere. If the area is low enough that the water only evaporates the salt builds up until you get something like the salt flats
Phrak
#7
Jul6-09, 11:36 PM
P: 4,513
Quote Quote by Proton Soup View Post
i never thought about it before, but it seems like it would take a lot of salt. or seawater.
I think similarly. How many tonnes of this precious commodity would it take per acre? If sea water, it would still be a staggering amount to poison all the fields supporting Cathage, I'd think.
Office_Shredder
#8
Jul7-09, 12:21 AM
Emeritus
Sci Advisor
PF Gold
P: 4,500
Wikipedia directly answers the example of Carthage actually

http://en.wikipedia.org/wiki/Salting_the_earth
binzing
#9
Jul7-09, 05:16 PM
P: 252
The other thing I find odd about this is that for many thousands of years, salt was one of the most valuable commodities in the world, so why would they just spread it on the ground?
Proton Soup
#10
Jul7-09, 05:28 PM
P: 1,070
Quote Quote by binzing View Post
The other thing I find odd about this is that for many thousands of years, salt was one of the most valuable commodities in the world, so why would they just spread it on the ground?
scarcity depends on location. the story of Shechem in the wiki link above is more credible since it is near both the mediterranean and dead seas.
bucher
#11
Jul7-09, 05:44 PM
P: 77
For the long term effects of the salt, it's not the salt itself that prevents plant growth. The salt causes the microscopic alignment of the soil particles to all face the same way (like metal shaving under a magnetic field). This causes water to not penetrate as deep into the soil and hinders the distribution of nutrients from the soil.

Even after the salt itself is gone, the effects still remain until the soil can realign itself to support plant life.
noblerare
#12
Jul7-09, 06:14 PM
P: 44
Quote Quote by bucher View Post
For the long term effects of the salt, it's not the salt itself that prevents plant growth. The salt causes the microscopic alignment of the soil particles to all face the same way (like metal shaving under a magnetic field). This causes water to not penetrate as deep into the soil and hinders the distribution of nutrients from the soil.

Even after the salt itself is gone, the effects still remain until the soil can realign itself to support plant life.
That's interesting. I did not know that soil had its own alignments and directions. Could you elaborate more on this? Are you saying that the soil is supposed to face random directions so that the water can seep deeper into the soil?
bucher
#13
Jul7-09, 08:35 PM
P: 77
I'll elaborate some more. If you were to take a grain of soil and grind half of it away and look at it under a microscope, you'll find that there will be grains in the piece of soil just like grains in wood. These grains all point in different directions. Because of this, water can seep through the grains if the soil gets wet. This way the soil can absorb the water along with distributing it further underground.

The addition of salt causes the grains in the soil to align the same way due to the ionization effects the salt has. With this I should note that you don't necessarily need NaCl to "burn" the earth. Any salt will due but the "burning" itself depends on the ionization effects of the salt.

With the grains of soil having the same alignment throughout itself, water will not penetrate the soil particle. Instead, it will just pass over. This means that the water will spread out and stay near the surface of the ground and easily evaporate when in the sun. Since the soil is aligned the same way, nutrients in the soil are trapped and have a difficult time getting out to the plants.

Gradually over time, though, rain eventually washes away the salt and eventually the grains of soil lose the affects from the ionization of the salt.

I did a project that delt a little with this so I had to research this topic.


Register to reply

Related Discussions
Rotation of earth and weight of an object on the earth Classical Physics 8
Was Mars the Earth of the past and Venus the Earth of the future? General Discussion 6
Salting in? Salting out? Chemistry 5
Did the core of the Earth collide with the Earth billions of years ago? Earth 10
Salting out/salting in Chemistry 0