它可以在下雨时被冲刷掉，也可以释放到大气中，而磷与钙和铁结合，可以在土壤中保存数千年。
It can be washed out when it rains or it can be released to the atmosphere, whereas phosphorus combines with calcium and iron, and can be preserved in the soil for thousands of years.
雨把所有的灰尘都冲刷掉了。
并且由于丰富的表层土被冲刷掉，土地侵蚀威胁到农作物产量。
And because it washes away rich topsoil, erosion can threaten crop yields.
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