What is the purpose of the state of
the union address?

The address fulfills the requirement in Article II, Section 3 of the U.S. Constitution for the President to periodically "give to the Congress Information of the State of the Union, and recommend to their Consideration such measures as he shall judge necessary and expedient."

Explanation:

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.