Originally written by Ruth Beck, former SDSU Extension Agronomy Field Specialist.
Crop rotation has long been considered an important farm practice. In 2013 producers had to stray from their well thought out crop rotations when the winter wheat crop in South Dakota failed. This may still be affecting many producers in central and western South Dakota. Crop rotation, or the planned sequence of specific crops in a field, can require additional planning and management for farmers. However the benefits of good crop rotation are numerous and include reduced soil erosion and improved soil water management, soil tilth, and fertility.
Crop rotation can also reduce pest issues and reliance on pesticides. Rotations also allow farmers to spread their workload and better utilize labor and machinery resources. The risk from weather related incidents can also be reduced with a good crop rotation.
There are a number of basic principles to consider when determining a crop rotation. One basic principle is crop water use. Crops such as sunflowers and corn are considered high water use and can draw soil water to very low levels at harvest The success of crops planted after a high water use crop will be determined in part by weather and the amount of precipitation received, caught, and infiltrated between harvest of the high-water-use crop and seeding and/or moisture sensitive periods of the succeeding crop. In all cropping systems water use must match water availability. If the system is not sufficiently intense problems such as water logging, saline seep formation, nutrient loss, traffic ability problems, etc. are common. If the system is too intense, poor yields due to water stress or stand establishment problems are likely.
Another determining factor in crop rotation decisions are pests. Crop rotation has long been advocated as an excellent way to break the cycle of disease, insects and weeds. It is commonly accepted that yields of crops grown in rotations are 10% (or more) higher than yields of crops grown in a monoculture. This yield benefit is sometimes referred to as the rotation effect. The common thought is that this benefit is the result of a number of factors working together, among those, is a reduction in disease and other pest issues.
Crop rotations will be more successful if they include three or four crop types (cool-season grass, cool-season broadleaf, warm season grass and warm-season broadleaf). Also rotations that are not consistent in terms of either interval or sequence provide the best protection against shifts and biotype resistance. In other words rotations such as wheat-canola or wheat-canola-wheat-pea are consistent in both interval and sequence. Wheat always occurs in alternate years and always follows a cool-season broadleaf. Rotations such as spring wheat-winter wheat-pea-corn-millet-sunflower are not consistent in either interval or sequence. Rotations should have crop type to crop type intervals of a minimum of two years somewhere in the rotation.
There are a number of common plant diseases where recommended best control method is listed as crop rotation. In these circumstances crop rotation can lead to a healthier, more resilient crop by reducing and preventing the transmission of disease. However there are a few situations where the cycle of plant disease can be aggravated by crop rotation. The one that comes to mind is wheat after corn or sorghum. Corn or sorghum grown prior to wheat can result in an increased incidence of fusarium head blight (FHB) in wheat. FHB can be very detrimental to both yield and quality. This crop sequence can also lead to increased root and crown diseases in the wheat. Root and crown disease can be difficult to identify until late in the season. In any event there is no cure and, depending on the situation, these diseases can substantially reduce yields in wheat. Therefore it is not recommended to follow corn or sorghum with wheat in a crop rotation. Barley and oats present less of an issue but sequencing these crops behind corn or sorghum is not ideal. Large-seeded broadleaf crops like peas, soybeans, sunflowers, etc. do well following warm-season grasses.
Planting too many low residue (low in carbon content; sunflowers, peas, soybeans) crops in a rotation and especially in sequence can leave fields susceptible to erosion from wind and/or water. It is important that we have corn and wheat (also consider oats and sorghum) relatively frequently in all our annual crop rotations as these provide good soil cover. These crops also leave residue that is high carbon content. Residues high in carbon are better at building soil organic matter.
Another important consideration for farmers in determining crop rotations is work load. Equipment and labor can cover more acres with crops that are seeded, sprayed and harvested at different times throughout the growing season.
Overall crop rotation is known to be a beneficial management tool. However each farm will have to determine its own specific rotation dependent on soil, climate, equipment and human resources.