What Are Crop Rotations?
Farmers change the crops they are growing in a particular field from year to year. While the specifics of the practice can vary, the purpose of the practice is to reduce erosion, enhance the fertility of the soil, and ultimately increase crop yields. In 2015, a grower in Virginia was able to break the 500 bushel yield barrier on his corn using a double-crop rotation of winter wheat, soybeans and corn http://www.genesis.ag/crops
History of Rotating Crops
The practice of rotating crops has enjoyed a long history.
Farmers in the middle east practiced crop rotation over 8 thousand years ago by rotating between cereal crops and legumes. The legumes, through the nodulation of symbiotic nitrogen fixing bacteria leave a nitrogen surplus once the crop is tilled into the soil. The nitrogen surplus would be used up by the following wheat, oat or barely crop.
Late in the middle ages, farmers settled into a three-crop rotation where winter wheat was followed by spring legumes and one field was laid fallow. The fallowed field would “rest” and some of its fertility would be restored as organic matter from the previous years harvest were reintroduced into the soil through the process of decay.
A key breakthrough that enabled the British agricultural revolution was the introduction of four-field crop rotation. The system was championed by Charles Townshend and introduced the idea of fodder and grazing crops for livestock. The livestock, while grazing would deposit manure in the field and work the manure in with their hooves, making for a more enriched soil the following year. The four-field crop rotation is credited with boosting agricultural yields by as much as 30%.
Many conventional farmers continue to practice some form of crop rotation in order to minimize fertilizer expenses and reduce pressure from diseases which become more prevalent after years of continuous cropping. However, in an effort to push average yields even higher, many farmers have gone away from leaving fields fallow in favor or replacing the nutrients depleted from the soil with fertilizers and liming materials.
Wikipedia has an excellent article on the history and importance of crop rotations: https://en.wikipedia.org/wiki/Crop_rotation
Decisions on Appropriate Rotations
How the farmer decides to rotate his crops will depend on a number of factors, including;
- desire to build organic matter
- weed management
- pest pressure
- nutrient deficiencies
- erosion control
- prevailing markets
The following crops are some general classifications around which farmers build their rotations. Specific species within these specifications will be determined based on previous experience with the crop, weather, soil type, available moisture and market factors which will influence the farmer’s potential R.O.I.
- Row Crops — The most common of these include corn
- Legumes — The most common of these include soybeans, peas and peanuts
- Cereal Crops — These include wheat, barely, oats, & rye
- Cover Crops — These include radishes, wild carrots, red clover and other legumes for adding nitrogen to a depleted soil