The growing of the same crop on the same land continually is considered poor practice, which can result in decreased yield and quality due to a build-up of weeds/pests, soil compaction and ‘tired soil’, soil depleted of nutrients. These complications can lead growers to try and overcome them through increasing their use of fertilisers, herbicides and pesticides, and irrigation, which in increase inputs and environmental problems. For these reasons it is recommended that growers use at the minimum a three year rotation cycle. A three year rotation cycle could be; corn in the first year, legumes in the second and cole crops in the third, repeating this cycle every three years.
Well-designed crop rotations will help suppress weeds and pest, and improve soil condition. One way crop rotation suppresses weeds and pests is through disrupting their cycle of reproduction.
The practice of crop rotation is enhanced through the addition of organic matter from forage crops or green manure which rebuilds soil structure and replaces lost nutrients, especially nitrogen. Organic matter also improves water and air balance in the soil which produces healthier and more vigorous crops which are better able to resist weeds and pests, and environmental pressures.
A well-designed crop rotation system would include the following:
Crops with deep roots along with shallow-rooted crops
Crop sequence, such as nitrogen dependant crops followed by nitrogen fixing crops
Crops which have different weed/pest susceptibilities
Forage legumes (clover, alfalfa)
Tomatoes should not be grown in the same soil two years running nor be rotated with other nightshades vegetables such as peppers, eggplants or potatoes.
Crop rotation assists in breaking and disrupting weed, insect, and disease cycles, maintaining and improving soil quality and helping to cycle nutrients and improve soil fertility. An agronomic and environmental advantage of crop rotation is through alternating nitrogen-dependent crops such as corn with nitrogen-fixing crops such as legumes hence reducing the need for nitrogen fertilizers. Grain-legume rotations have shown increased yields regardless of fertilisation rates, allowing for savings in both fertilisation and herbicide/pesticide application costs.
Complimentary rotation of closely grown crops with row crops increases vegetative cover decreasing soil losses due to water and wind erosion, which reduces runoff into waterways of herbicides and nutrients. For most effective disruption of weed, insect and disease cycles is obtained through inclusion of legumes, row crops, and small grains.