Image Caption: Effects of crop rotation and monoculture at the Swojec Experimental Farm, Wroclaw University of Environmental and Life Sciences. In the front field, the “Norfolk” crop rotation sequence (potatoes, oats, peas, rye) is being applied; in the back field, rye has been grown for 45 years in a row. Credit: Leslaw Zimny/Wikipedia
Crop rotation is the practice of planting different types of crops (also known as polyculture) in the same location in subsequent seasons. Utilizing crop rotation allows the field to remain productive versus going fallow and also reduces the need for artificial fertilizers. Crop rotation replaces nutrients that were depleted by the previous crop. Crop covers, such as clover, is used as green manure in order to replenish nitrogen and other nutrients.
Rotation planting also aids in preventing a build-up of pathogens along with pests that are commonly found in single (monoculture) crop plantings, thereby breaking the cycle of the pests. Root-knot nematode is one example found in warm climates and sandy soils. High levels of root-knot nematode found in soils cuts off the circulation from the plant and its roots thereby damaging the productivity of the plant. In order to avoid soil fumigation to rid the soil of the nematodes a crop that is not a host will need to be planted in the subsequent season.
Weeds will also need to be controlled as well. For example, ergot fungi are found growing on cereal grains which is then difficult to separate once harvested. Ergot fungi produces alkaloids that are released into the soil contaminating the grains. Consumption of the contaminated grain can have serious side effects such as convulsions. Crop rotation can be used to break the cycle of the ergot fungi.
Choice of crops
The choice of cash crop depends on many variables such as soil type, climate, and the amount of precipitation (or other access to a water source such as a canal) that the region where planting has to offer. The cash crop also depends on if it is a grain crop or crop used for forage. For instance, soybeans will follow corn for a grain crop and alfalfa will follow corn when used as forage. Once the cash crop has been decided, the subsequent rotation crop will also need to be considered in order to replace the right nutrient that was depleted by the cash crop. Depletion of nitrogen can be replaced by using plantings of peas or beans (legume family) in the subsequent year.
Intercropping, also known as companion planting, is usually accomplished on a smaller scale as found in home gardening. For instance, tomatoes can shade carrots which also loosen the soil below the carrots to allow the root to grow.
Incorporation of animals
Integrating farm animals into crop rotation is becoming more popular in areas such as in Sub-Saharan Africa. Residue from crops is used to feed the animals and the animals provide the manure needed to replenish the nutrients as well as provide draft power to the people. Animals such as sheep, cattle, and goats will have the added benefit of providing milk, fibers, or meat which would be beneficial during hard economic times. Integrated farming has been conducted in the United States for centuries.
Diversification of production costs is an added benefit for the large scale farmer reducing the overall financial risk.
Crop rotation can reduce the effects of water run-off in the form of erosion. Different methods are used in different regions depending on the susceptibility to erosion. Some farm management suggest reduced-to-zero tilling along with crop rotation to reduce the impact from rain, sediment detachment and ultimate soil loss if the region has significant rain fall.
Areas that are not susceptible to erosion can withstand a more rigid approach to crop rotation, which will allow for plant growth along with soil cover. A more flexible approach will be needed in areas that have erratic climate conditions in order to promote adequate soil cover.
Another method of reducing soil loss is leaving crop stubble, such as corn stalks, on top of the soil. The plant stubble will cover the soil reducing the flow of run-off from rains which in turn reduces the amount of sediment run-off or soil loss.