Using the same soil to grow different crops. Interrupts cycles of weeds, diseases, and insects; builds organic matter, improves soil structure. Useful rotations: nutrient-grabbing crops like corn, celery, and potatoes with those that need less, like garlic, mustard, or shallots; and shallow-rooting crops with deep ones. (Soil improvers: broad beans, lima beans, peanuts, peas, shell beans, snap beans, soybeans. )