crop rotation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The successive planting of different crops on the same land to improve soil fertility and help control insects and diseases.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun agriculture A farming practice in which the same land is used to grow different crops in successive seasons or years (when once the land would have been left fallow); used to prevent erosion and increase fertility.