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  • Dry, drought-prone regions of the world produce nearly a third of the global

  • food supply, and many of the crops in these regions are in danger of going

  • thirstynot only because the soil they grow in contains too little water, but

  • because it contains too much salt. Salt is a natural part of soils everywhere

  • it forms from minerals weathered out of rockbut in wet climates, most of it gets

  • dissolved by percolating rain and carried down to the groundwater below.

  • In dry climates, on the other hand, percolating rainwater rarely makes it that far

  • most of it gets soaked up by the deep roots of native plants, causing its salts to

  • precipitate out and gradually accumulate in the soil below.

  • This salty layer isn't a problem as long as both the plants and the water table stay where they are,

  • but when native vegetation gets swapped out for shallow-rooted crops, more rainwater

  • makes it all the way to the groundwater, causing the water table to rise.

  • On its way up, it dissolves the salt deposit, bringing salty water to crops' roots.

  • And here's where the hydration problem comes in: individual molecules of

  • salt are a lot bigger than molecules of water, so they get stuck in narrow

  • junctures in plants' plumbing and cut off their water supply. At best,

  • a plant that can't hydrate properly grows slowly; at worst, it dies.

  • And irrigation just exacerbates things: irrigated water comes from rivers and lakes and is slightly

  • saltier than rain, so it adds salt directly to the soil while speeding the

  • water table’s rise. We humans have run into this problem before

  • historians believe salty soils contributed to the fall of ancient

  • Mesopotamia. Were seeing some effects today, too: as much as one quarter

  • of all irrigated dry farmland on Earth experiences reduced yields due to salt.

  • But even without additional water, groundwater comes up fast: for example,

  • when forests in southwestern Australia were converted into non-irrigated farmland,

  • it took just 12 years for the water table to rise 18 meters to the surface.

  • One way farmers in dry regions deal with this problem is by periodically

  • flushing their soils with enough freshwater to remove the salt.

  • This workstemporarilybut requires a lot of water,

  • sometimes more than is used on crops over an entire growing season.

  • A better option is to plant thirsty, deep-rooted trees and shrubs, which can

  • soak up most of the percolating water and reverse the rising water table.

  • In Australia, native trees planted amongst conventional crops slurped up so much

  • water that the water table fell 3 meters in a decade, taking its load of

  • dissolved salts with it. And farmers in Uzbekistan achieved similar results by

  • switching back and forth between crops and native shrubs every few years.

  • But regardless of whether we alternate them spatially or temporally, we will most

  • likely need to rely on drought-adapted native plants to help preserve the large

  • swaths of dry, increasingly-salty farmland that produce a third of the world’s food.

  • Because in this case, if we salt our food before we taste it,

  • we might not get to taste it at all.

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Dry, drought-prone regions of the world produce nearly a third of the global

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B2 中高級 美國腔

我們的食物鹽分過高,而不是你想的那樣。 (We're Oversalting Our Food, And It's Not What You Think)

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