Mesopotamia was so good for growing crops because of one incredible natural phenomena: the fact that whenever the nearby river flooded, it deposited nutrient rich soil. Though the river flooding itself wasn’t good for the crops, the aftermath was.
Most crops will fail with too much water (rice is one exception that needs a lot of water to grow properly), but the nutrient rich soils helped every kind of crop grow better. Some crops in particular need a lot of nitrogen or something else, and deplete the soil of said nutrient when they grow. That’s why you should move crops around every year; the crops there the year before probably depleted most or all of the soil’s stores of a particular nutrient.
