Indo-european tribes came to the fertile crescent from the steppes north of the?

byzantine empire is the answer i think you are looking for.

hope this : )

crop rotation kepy different plants in the soil instead of once constintly. when switching out plants you have different nutrients being absorbed at different speeds and different roots growing differently therfore the spoil and water flow have to adapt and carry fresh nutrients to carry the constant changes that were going on in the soil.