Salt the Earth

"I will personally burn everything I’ve made to the fucking ground if I think I can catch them in the flames."

- Gabe, Penny Arcade

Salting the earth is an act to curse the land and render fields incapable of crop growth, often used in ancient times as a symbolic act on top of various other scorched earth tactics to indicate the desire of the victor to completely eradicate the enemies' ability to reconstruct themselves after the war.

So as a trope, characters will often have an analogous action, sometimes literally salting the earth, which performs as a symbolic act to indicate their embrace of scorched earth tactics and the increase of hostilities beyond it. The act can be a movement across the Moral or Despair Event Horizons, increasing the threat of a character, making the stakes truly a matter of survival and making the lack of forgiveness or remorse clear. So it is that the act can occur at a pivotal moment in the middle of a war or as the final blow at the end of one.

The action was common in the ancient Middle East and extended to the Middle Ages. The thing to note, though, is that salt was costly then. Heck, even a bad winter can give us difficulty in getting salt supplies out to spread on the roads. So in these tales, look at salt as not just something bad for the crops but also as something with attributed mystical powers and that you probably aren't going to spread over an entire field, leaving just the corner of some garden being ploughed for the symbology of it. They knew their tropes, even then.

Enough salt will decrease the fertility of the land. This was discovered first in Mesopotamia, when salts left from irrigation reduced fertility enough that whole civilizations collapsed. Unlike the symbolic versions practiced by the Romans, this involved centuries of salt deposits building up.

Film

 * Cobalt bombs (see below) were popularized in the 1964 film Dr. Strangelove. The element added to the bombs is referred to in the film as 'cobalt-thorium G'.
 * The second Planet of the Apes movie had one.
 * Idiocracy: Not the result of malice, but stupidity. A Gatorade Ersatz got a law passed at some point to replace all water with their sports drink, because it has "electrolytes", which is "what plants crave". For those not quite scientifically savvy enough to see the mistake (they sure as hell didn't), electrolytes are a type of salt. It's likely that they would've starved to death if Joe hadn't come around and suggested they use water. ("You mean from the toilet?")
 * In The Ruins, the people guarding the titular ruins do in fact salt the earth around the pyramid. Very, very heavily, and for excellent reasons. It's unfortunate that they can't explain them.
 * In the backstory of Tron: Legacy, Clu poisoned the Simulation Sea to stop any new Isos from coming to life. Then he started his campaign of genocide against the rest.

Literature

 * Neville Shute's 1957 novel, and subsequent 1959 movie, On the Beach, features the cobalt bomb (see below).
 * In the novel The Crash of '79 by Paul Erdman, the Israelis use cobalt bombs on Saudi Arabia's oil fields to make them "off limits" to humanity for at least 30 years and end the Arab power over oil.
 * The Pak in Larry Niven's Protector are a human forerunner whose third stage of life is a superhuman keyed to protect its own as identified by scent, and so they're at war whenever one of them can see an advantage to their family. To protect the central Library that contains all the knowledge the families are willing to share, (and is tended by protectors who have lost their families) the land around it is seeded with radiocobalt to make the area undesirable.
 * In the Wing Commander novel Fleet Action, the Kilrathi build a fleet of super carriers and begin a seemingly inexorable push into human space. Along the way they bombard any human planets with Strontium-90 clad thermonuclear weapons that ensure that the planets will be uninhabitable. Even if the Kilrathi had succeeded, they would have gained little because they would have had no use for the conquered territory. Of course, this was precisely the point, and was the cause of an Enemy Civil War among the Kilrathi that ultimately prevented Earth from being obliterated.
 * The Bible, Judges 9:45 - Abimelech conquered the city of Shechem and sowed it with salt. NIV translation: "All that day Abimelech pressed his attack against the city until he had captured it and killed its people. Then he destroyed the city and scattered salt over it."
 * Mentioned in passing in The Eagle of the Ninth, and downplayed a bit. The protagonist reflects that the arable land that has been ploughed with salt in reprisal for an attack on the local garrison will be useable again within a few years, but nothing can replace the dozens of young men killed in the fighting.

Live Action TV
"Mr. Ward: "Burn it down, gentlemen. Burn it down and salt the earth.""
 * Sue Sylvester on Glee: "I sold my house to a nice young couple and salted the earth in the backyard so that nothing could grow there for 100 years. Know why I did that? Because they tried to get me to pay their closing costs..."
 * The government's final disposition of The Initiative, in season 4 of Buffy the Vampire Slayer:

"Kira Nerys: Dukat wanted the station back? He can have it!"
 * Star Trek: Deep Space Nine: When the Federation is unable to hold Deep Space Nine against the Dominion and Cardassian forces, they evacuate it. As soon as they're gone, Kira Nerys destroys the station's computer systems, effectively crippling it for months.

""Hey you bastards... John Crichton was here!""
 * The Cardassians trashed the station on their way out just before the beginning of the series. They also exploited Bajoran resources extensively enough that there was famine when they left due to ruined potential farmland (probably on purpose).
 * The crew of Moya do something analagous in the season 1 finale of Farscape: exploding a ship in the atmosphere of a Peacekeeper moon, which ignites the moon's entire atmosphere.


 * The theme song to Firefly uses it as a form of defiance. Their enemies can "burn the land and boil the sea," but they'll still have the sky.

Tabletop Games

 * In the history of the High Elves of Warhammer, there was a civil war that split the nation. The point of no return when two different races would form came when a king whose family had been killed by the enemy moved to scorched earth tactics and would salt the fields of their lands on the continent, driving them onto a completely different land.
 * The Magic: The Gathering card Rain of Salt.
 * Not to mention the much more literal Sowing Salt.
 * In the backstory of Vampire: The Masquerade, the vampires of Rome had the lands of Carthage salted to trap their enemies, who have become one with the earth to hide.

Video Games

 * In the Fallout: New Vegas DLC Honest Hearts, this is where the villain Salt-Upon-Wounds gets his name.

Western Animation
"Ned: Homer, why did you pick all the flowers out of my garden? Homer: Sorry, can't make a float without flowers! Ned: Well, I can understand that, but did you have to salt the ground so nothing will ever grow again? Homer: *starts giggling*"
 * In the Three Panel Soul where one software developer drops a match and some salt shaker salt as he quits. It's done "in the spirit" of the idea.
 * "That's not exactly burning and salting the ground as you leave.." "I'm really not that mad anymore"
 * When Homer Simpson needed flowers for a parade float he took all of the ones from the Flanders garden. Flanders didn't really have a problem with this, but questioned the point of salting the soil so nothing would grow again.


 * This was essentially Fire Lord Ozai's plan during Sozin's Comet in Avatar: The Last Airbender. Tired of the Earth Kingdom not being oppressed enough, he intended to have a fleet of dirigibles carrying comet-enhanced firebenders burn the entire kingdom to the ground. Then again, given that he is insane, and his sadistic daughter gave him the idea, it's likely less "salt the Earth" and more "kill them all."

Real Life

 * The Cobalt bomb is a type of "salted bomb" (a bomb intended to contaminate an area by radioactive material, with relatively little blast) originally proposed by physicist Leo Szilard, who suggested that it would be capable of destroying all life on Earth.
 * Nearly all the land between Berlin and Moscow was scorched and salted twice in World War II: once by the retreating Russians and two years later by the retreating Germans.
 * The city of Palestrina in the Papal States (now in Italy) revolted in the 1290s. When Pope Boniface VIII's forces defeated the rebellion, he ordered the city symbolically plowed and salted. This is one of several reasons Dante put Boniface in Hell.
 * The Tavora noble family in Portugal was convicted in 1759 of an attempted assassination of the king (Joseph I) the previous year. They were executed, their palace in Lisbon was destroyed and the land where it had stood was salted.
 * Similarly, when a Brazilian revolutionary plot against Portugal (at that time Brazil was a Portuguese colony) was put down, the leader, Tiradentes, was sentenced to death, his house to be torn down and the land where it stood salted.
 * The Romans were terribly fond of this. The most famous example was their treatment of Carthage, with whom the Romans fought numerous wars before emerging victorious. They destroyed Carthage and salted the earth to make sure nothing could ever grow in its place. Julius Caesar later founded a new Carthage on the same spot, mainly to prove that he could.
 * This was a metaphor for Rome's destruction of the city, and even then wasn't thought up until much later. Most of the farmland surrounding Carthage was actually given to Roman veterans of the Punic Wars as a retirement pension.
 * When the Mongols sacked Baghdad, it's said that a year later you could gallop a horse across where the city had been, for no stone lay atop another.
 * The infamous Hama massacre of 1982, where the Syrian army besieged the city for 3 weeks, killing somewhere between 17,000 and 40,000 people. It's widely considered the Moral Event Horizon for the Ba'ath Party and Hafez al-Assad.