Crop rotation is the practice of growing a series of different crops on the same land in successive seasons. It is a type of polyculture. The land is divided into 3, 4 or more sections, and different types of crops rotated each year to confuse pests and renew soil. Specifically legumes can be planted to fix nitrogen into the soil and benefit the planting of brassicas and other crops the following year. Similarly, crops that do not appreciate large amounts of fresh manure, such as carrots and parsnips, can be planted on ground that has been manured the previous year for crops such as onions, salads and legumes.

Benefits

Rotating crops can add nutrients to the soil, increasing soil fertility and crop yield. A traditional element of crop rotation is the renewal of nitrogen by using green manure in sequence with cereals and other crops. Also legumes have nodules on their roots which contain nitrogen-fixing bacteria called rhizobium bacteria. This can be followed by a crop that needs nitrates, such as potatoes or cereals. Crop rotation also reduces the build-up of pathogens and pests that often occurs when one species is continuously cropped. It can also improve soil structure and fertility by alternating deep-rooted and shallow-rooted plants. Lastly it can help to reduce soil erosion.

Features

Organic crop rotation systems can vary hugely but all involve a fertility building phase followed by a productive phase. It is the nitrogen fixing ability of legumes, especially clovers, vetches, sainfoin and lucerne (alfalfa) but can also include various beans and peas. Clovers and other legumes can be undersown with cereals.

Ground rules

• Use crop sequences that promote healthier crops, help in controlling weeds.
  
• Deep rooting crops should follow shallow rooting crops
  
• Crops which develop slowly and are therefore susceptible to weeds should follow weed suppressing crops
  
• Alternate between:
  
• crops with high and low root biomass
  
• leaf and straw crops
  
• autumn and spring sown crops
  
• crops of different species or families
  
• nitrogen fixing crops and nitrogen demanding crops
  
• Catch crops, green manures, and undersowing should be used to keep the soil covered
  
• Grow some crops that will leave a significant amount of residue.
  
• Use variety and crop mixtures when possible. When growing a wide mix of crops try grouping into blocks according to plant family, timing of crops, type of crop (root vs. fruit vs. leaf), or crops with similar cultural practices.
  

Publications

Crop rotation on organic farms

http://www.sare.org/Learning-Center/Books/Crop-Rotation-on-Organic-Farms

Videos

Organic Crop Rotations: Conservation Benefits. 90 mins.