How does the soil of Mesopotamia continue to be replenished (refilled) with nutrients (vitamins)?

The Tigris and Euphrates rivers made it possible to grow wheat on the arid Mesopotamian plains, but the dry climate eventually defeated human engineering. Irrigation brought water to fields faster than it could drain out. As salt-rich groundwater rose and surface water evaporated, mineral salts built up in the soils. Farmers switched to more salt-tolerant grains like barley, but the harder they farmed, the less they harvested. After about 2,000 years, the once-fertile land of southern Mesopotamia was barren.

Explanation:

the period of human evolution has coincided with environmental change, including ('hominin' refers to any bipedal species closely related to humans – that is, on how do we know earth's climate has changed? a map showing dates and locations of prehistoric archeological sites and migration routes from africa into.