I remember reading recently that in the Antebellum American South, part of the reason that white southerners wanted to expand slavery westward is that cotton agriculture would cause soil exhaustion. After growing cotton on a given piece of land for a few years, the soil would be degraded in such a way that one could not profitably grow cotton on the given piece of land until the soil was treated somehow. Once the soil was exhausted on a cotton planter's plantation, the planter would buy more land out west and move with his slaves to the planter's new lands out west rather than restore the soil on his plantation back east. How does cotton agriculture cause soil exhaustion chemically? I mean, does growing cotton make the soil too acidic or too alkaline? Or, if cotton growing does not cause soil exhaustion due to pH, how does cotton growing cause soil exhaustion? Once the soil exhaustion has occurred on a piece of land due to cotton agriculture, how do farmers restore the soil? If the answer is crop rotation, what crop restores the soil if the soil exhaustion was due to cotton agriculture? Or do cotton farmers restore exhausted soils by using fertilizers such as manure or what?