To reduce in amount by using up.
Example:
Years of farming on the same plot of land had left the soil depleted of minerals.
The de- prefix often means "do the opposite of," so deplete means the opposite of "fill." It can mean merely a lessening in amount; thus, food supplies can be rapidly depleted by hungry teenagers in the house. However, deplete usually suggests a reduction that endangers the ability to function. Desertions can deplete an army; layoffs can deplete an office staff; and too much exercise without rest can deplete a body's strength.