Crop rotation is “The practice of alternating the annual crops grown in a specific field in a planned pattern or sequence so that the crops of the same species or family are not grown repeatedly without interruption on the same field”. -US National Organic Program definition-
OR leaving soil in the best position it can be for continuing/next crops – that includes cover crops, rotations, green manures, catch crops etc.
BENEFITS OF CROP ROTATION
- Preventive Pest Management
Crop rotation may limit the growth of populations of agricultural pests including insects, nematodes, and diseases caused by bacteria, viruses, and fungi through regular interruption and replacing crop host species with different plant species that do not serve as hosts. The use of specific crop and cover crop rotations may also be used to control pests through allelopathy, an interference interaction in which a plant releases into the environment a compound that inhibits or stimulates the growth or development of other organisms.
- Reduced Weed Competition
Carefully designed crop rotations may also serve to outcompete problematic weed species through shading, competition for nutrients and water, and/or allelopathy.
- Distribution of Nutrient Demand Placed On Soil by Crops
Different crops place different nutrient demands on the soil.
- Making Efficient Use of Nutrient Inputs
Cropping species that access nutrients from different depths within the soil horizon may make the most efficient use of nutrient inputs. Efficient use of agricultural nutrients may further prevent nutrient losses/leaching and associated environmental pollution.
- Nitrogen Fixation
Annual cover crop rotations using nitrogen-fixing (legume) cover crops may contribute significant amounts of nitrogen to succeeding crops as well as adding organic matter to the soil.
- Improving Soil Quality
Cover crop rotations allow soils to remain undisturbed for various periods of time during which the processes of soil aggregation can take place. The use of a perennial grass rotation lasting 6 months to one year or more may significantly contribute to organic matter accumulation, stimulate soil biological activity and diversity, and improve soil physical properties.
- Increased Crop Yields
The rotation effect – Yield of crops grown in rotation are often higher than those grown in monocultures, even when both systems are supplied with abundant nutrients and water. Growing a diversity of crops in a given year spreads out labour needs throughout a season. The diversity of crops reduces the economic risks caused by variations in climate and/or market conditions.
TEN BASIC PRACTICES OF CROP ROTATION
Rotate the location of annual crops each year. This is especially true for crops in the Solanaceae family (e.g., peppers, eggplants, tomatoes, potatoes, etc.). Do not follow one crop with a closely related crop species, as pests and diseases are shared by closely related crops. When growing a wide diversity of crops, attempt to group crops into blocks according to the following criteria:
- Plant family
- Similar timing/maturation periods
- Type of crop (i.e., root vs. fruit vs. leaf crop)
- Crops with similar cultural requirements (e.g., irrigation, plastic mulch, dry farmed, planted to moisture crops, etc.)
- Follow nitrogen-fixing cover crops and/or legume forage crops (e.g., clover, alfalfa) with heavy feeding crops (e.g., corn) to take advantage of nitrogen supply.
- Follow long-term crop rotations (e.g., 1-year perennial rye rotation or pasture rotations) with disease-sensitive crops (e.g., strawberries).
- In diverse annual production systems, heavy-feeding crops (crops with high nutrient demands) should be followed by medium-light or shallow-rooted crops, followed by deep-rooted crops.
- Always grow some crops that will produce and leave a large amount of residue/biomass that can be incorporated into the soil to help maintain soil organic matter levels.
- Grow deep-rooted crops (e.g., sunflower, fava beans, etc.) that may access nutrients from lower soil horizons, alleviate soil compaction, and fracture sub-soil, thus promoting water infiltration and subsequent root penetration.
- Use crop sequences known to aid in controlling weeds.
- Use crop sequences known to promote healthy crop growth (e.g., corn followed by onions followed by Cole/Brassicaceae crops) and avoid cropping sequences known to promote pests and diseases (e.g., monocultures in general or peas followed by potatoes specifically).
In conclusion, crop rotation is primarily about a cultural system that is based on natural principles. It is about building a fertile living soil and an environment that supports the healthy growth of plants and natural biological control—a situation where synthetic pesticides and fertilizers are unnecessary and even counterproductive.