Sorghum, being more drought tolerant than corn, is usually a better choice. If corn follows corn, the use of a rootworm insecticide may be necessary. Some farmers have extended the 4-year rotation to five or even six years. Producing a crop every year reduces land costs and delays the cost of summer fallowing at least one year. Soil conservation is also improved because during the fallow year conventional tillage practices are used to keep the soil weed-free and to prepare a seedbed for winter wheat.
Excess tillage reduces crop residues and exposes the soil to wind and water erosion.
Other reasons for extending the rotation and growing continuous no-till row crops may be to break the cycle of wheat diseases and to aid in controlling weeds. For Cephalosporium stripe, the 3-year rotation may not provide enough time to break the disease cycle. Since this pathogen can survive within residue of diseased plants, the infected fields should not be planted back to wheat for at least three years. Winter annual weeds, such as downy brome and jointed goatgrass, may be a problem in a winter wheat-fallow rotation. These weeds can be controlled best by killing the seedlings in the spring and growing either corn and sorghum or two sorghum crops before returning to winter wheat.