Back in the 18th century farmers would plant there crops and wait for them to grow and when they grew they would harvest them. When it came time to plant again they would plant the same crop in the same place. That was the problem, crops use the nutrients in the ground to help them grow, some crops will take different nutrients from the ground then others. If you plant the same crop in the same place all the time you will take out all the nutrients and kills the soil. This is where Crop Rotation came into play, in Crop rotation when you plant one crop one year and it uses some nutrients you plant a different crop in the same place to help replenish the nutrients taking from the ground and after that year you plant a different plant in that spot and so on until you get back to the plant you originally planted there, that helps keep the nutrients balanced and doesn't use up all of them. This "invention" helped the farmers be able to plant more and more crops and never have to worry about there soil.