Crop rotation comprises of splitting the garden into four or more sections and planting a different plant species in each section yearly. With a planned rotating schedule, the gardener can make sure that every section ultimately receives each plant family. Crop rotation prevents the spread of plant diseases, reduces insect invasions, and lowers the risks of erosion and weather damage. It also increases net profits, improves soil fertility, and balances the nutrients in the soil.

References:

http://www.dannylipford.com/vegetable-garden-crop-rotation-made-easy/

http://www.ag.ndsu.edu/pubs/plantsci/crops/eb48-1.htm