dirt.

塵埃。

Maybe that's because, most of the time, soil takes care of itself; decomposing plants and

可能是因為大多數時候土壤都會自我修復：分解的

animals and degrading bedrock produce new soil at roughly the same pace that wind and

動植物和降解的岩床，製造土壤的速度大致等於

water erode it away

風和水的侵蝕速度。

But this balance between soil formation and erosion is easily tipped.

但這種平衡很容易被破壞，

For millennia, the tiny Pacific island of Mangaia was covered in a thin layer of fertile

例如數千年來，太平洋上的Mangaia島上覆蓋著一層

soil, but after humans arrived around 2000 years ago, their slash-and-burn agriculture

肥沃土壤，但在約兩千年前人類抵達後，火耕農業

exposed the soil to the elements.

把土壤暴露在光天化日下。

Over several centuries, rain and wind swept virtually all the nutrient-rich topsoil from

數世紀後，風雨把營養豐富的表土

Mangaia's hillsides and concentrated it in just a few arable valleys, which people

集中沖刷到少數可耕種的山谷，

viciously fought over.

人們為此大打出手。

With less land to grow crops, people resorted to alternative food sources like rats—and

能耕田的地少了，人們開始尋找替代的食物，如老鼠、

even each other.

甚至吃人。

We're doing the same thing throughout the world today - not the part where we eat each

我們現在正對整個世界做一樣的事─不是指人吃人，

other, but the part where we farm the soil away.

而是我們讓土壤流失。

That's because we make for agriculture by clearing away deep-rooted native vegetation

我們為了農業把深根的自然植物砍掉，

and use hoes, plows, and tractors to loosen the soil, making it easier for wind and rain

用鋤頭、犁和牽引機翻鬆土壤，讓風雨更易將其帶走。

to sweep away.

用鋤頭、犁和牽引機翻鬆土壤，讓風雨更易將其帶走。

And we grow mostly shallow-rooted crops that are no good at holding onto soil, and that

我們種的農作物根大多較淺，不易固定土壤，

get stripped away during harvest, leaving fields bare for much of the year and at the

收成後還會被剷掉，讓裸露土壤長年裸露在

mercy of the elements

風霜雨雪之下。

As a result, the world's farmlands lose soil 50 times faster than new soil can form.

結果全球農地流失土壤的速度比生成快50倍，

That extra erosion adds up to about 8 billion pickup trucks of soil moved annually from

額外被侵蝕的泥土，每年都可填滿80億台敞篷卡車，

fields to places like the bottoms of rivers and behind dams - which are less convenient

從農地被送往河底或水庫─顯然不適合務農之處。

for farming.

從農地被送往河底或水庫─顯然不適合務農之處。

That soil loss reduces global crop yields by as much as if we took a California-sized

土壤流失減少了全球農作物產量，相當於每十年

swath of farmland out of production every decade.

荒廢一塊加州大小的農地。

Fortunately, we know how to bring erosion back into balance with the rate at which soil

好在我們知道如何讓侵蝕率降回與生成速度平衡：

forms: plow less often, and after harvest, leave plant parts behind or plant so-called

少犁田，在收成後把植物覆蓋在地上，或種植所謂

cover crops to, well, cover the soil as protection against water and wind.

覆土作物，以覆蓋土壤，保護其免受水與風侵蝕。

We can also incorporate trees or native plants that keep soil in place year-round.

我們也可以加入樹木或自然植被，常年穩固土壤。

Putting strategies like these in place can cut erosion by as much as 95 percent, helping

這些策略最多可減少95%的侵蝕，

keep crop yields high in the long run.

幫助產量常保穩定。

But in the present, they can hurt yields, because adding other vegetation to farm fields

但短期上這會降低產量，因為在農地上種其他植物

means less room for crops.

意味著較少空間種植作物，

As a result, we've been slow to make these soil-saving strategies the norm.

於是我們把這些策略寫入法規的速度十分緩慢。

If we can't keep the farmable soil on our farms, human civilization won't immediately

如果我們不把土壤留在農場，人類文明不會即刻崩毀，

implode, but we might end up fighting over the patches of land where that soil ends up,

但可能最後會因爭奪僅存的土壤而爭戰，

like the Mangaians, but on much, much bigger islands.

如同Mangaians島，但規模遠超乎於此。

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