Crop rotation is the systematic way of deciding what to plant in your organic vegetable garden year after year. It is also beneficial for organic farmers who grow crops on large scale. The goal of crop rotation is to manage the fertility of the soil and reduce problems related to insects and pests.
Different crops have different nutritional requirements. The soil balance also gets affected differently with different crops. Some crops like tomatoes or corn will drain the soil quickly out of nitrogen and phosphorus. So if you plant the same crop in the same location year after year, that plot of soil will run out of natural nitrogen and phosphorus. If you change the location each year, you can get the previous spot rejuvenated and thereby maintaining the overall balance of your soil. The general rule is to avoid planting similar variety of crop at the same location year after year. It is advisable to occasionally plant nitrogen fixing legumes and other leafy or fruiting crops before you plant nitrogen-draining crops.
Crop rotation is also beneficial in fighting certain kinds of pests and other diseases. Crops from the same family tend to attract similar kinds of pests and diseases whereas if you keep rotating the crop, you are avoiding the chances of the pests and diseases to grow stronger and multiply. It is always better to leave at least a year or two before you plant the same kind of vegetable or crop at the same location. Plant families are easily susceptible to pests and diseases.