Winter wheat yield is affected by production practices, pest management, fertility, and weather. One of the production practices having a major impact on yield is seeding date. Wheat seeded early uses more soil water in the fall, leaving less in the profile for yield production.
One research study showed a 50 bu/ac yield difference in the same field between a low-lying area with sufficient moisture and the rest of the plot where moisture was limited. Also, early planted wheat will face insect, weed, and disease pressures for a longer period in the fall.
The recommended seeding dates for Nebraska's winter wheat vary substantially from one end of the state to the other — from September 1 in the extreme northwest to October 1 in the southeast tip — and have been proven and verified through years of research and farmer experience. Some years an earlier seeding may have an advantage and some years a later date may have an advantage, but in the long term, the suggested seeding dates will give the highest average yield.
How Seeding Date Affects Tiller Development
Date of seeding greatly affects development of tillers in winter wheat, the source of as much as 70% of the grain yield in a normal year. Seeding during the optimum period enables wheat to form sufficient but not excessive tillers. Early seeding results in too many fall tillers, which may compete with each other, become diseased, and deplete soil moisture so that grain yields are low. Late seeding gives plants little time to develop tillers, resulting in an inadequate numbers of spikes (heads) for high yields the following spring.
Senescence and death may eliminate excessive tillers that form during the fall. Conversely, if too few tillers develop during fall, additional tillers may form during spring; however, the yield potential may differ between tillers that develop during fall and those that develop during spring.
Tillering also enables the plant to adapt to different conditions. Few tillers develop when moisture, nutrition, and other conditions are poor, whereas numerous tillers form when conditions are favorable. More tillers leads to increased yield potential. The recommended seeding date represents a goal for seeding completion. As farm size and the number of acres increase for individual farmers, so does the length of time needed to complete seeding. The goal should be to have all the wheat planted by the ideal date. Plan your field order for planting accordingly. For example, plant higher elevation fields and those containing sandy soil first and leave lower fields and those with higher clay content until last.
Recommended Planting Dates
Several factors were considered when developing the recommended seeding dates (Figure 1). In the Panhandle, the dates depend on elevation. Producers can determine the ideal date for each field by knowing the elevation. Using a starting point of September 15 for 3500 feet, one day should be added for each 100-foot decrease and subtracted for each 100-foot increase in elevation. For the rest of the state, September 25 or later seeding dates are recommended to avoid Hessian fly infestation.
The map (Figure 1) is a guide rather than an absolute deadline. Each producer should make changes to ensure the planting dates fit the conditions of his or her farm.
How Planting Date Affects Fertilizer Use
If the seeding date is delayed or growing conditions prevent or delay root growth to the dual placement fertilizer band, seed fertilizer placement is the preferred application method. Poor root growth for whatever reason limits root-fertilizer contact and tillering, which affects yield.
How Planting Date Affects Disease Problems
Delayed planting dates also may be due to a need to avoid wheat streak mosaic virus, Russian wheat aphid, crown and root rot, and too much fall growth. Excessive fall growth causes excessive moisture use and stress. There are several other reasons for planting early. One is to get adequate ground cover to avoid erosion from wind and water. Another is to get adequate plant growth to assure winter hardiness. A third reason is to quicken maturity the following summer and avoid excessive heat stress.
