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 (Table 1). 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. A grower who started seeding a field too early saw his yield double on the rest of the field where seeding was delayed a week due to rain.
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.
Research Shows Effect of Wheat Planting Date on Yield
A study by Kansas State University to determine how seeding date affects tiller development and productivity of winter wheat was conducted in a corn/soybean rotation at Hutchinson, Kansas. Two hard red winter wheat varieties, Jagger and 2137, were planted on four dates in the fall of 1995 (Table 2). The first date, September 28, was during the early part of the recommended period, September 26 to October 20. The second date, October 11, was one day after the Hessian fly-free date, and the last two dates, October 28 and November 11, were after the recommended period. Wheat varieties were planted at 60 lb/ac of seed in plots. Plots received 70 lb/ac of nitrogen and 25 lb/ac of phosphorus before planting and 50 lb/ac of nitrogen in late February 1996.
Data for Jagger and 2137 were pooled, since results for the two varieties were similar. Nearly equal numbers of seedlings emerged after all planting dates except October 11, when considerably more plants emerged (Table 2). Plants from the first two dates tillered profusely, developing most of their tillers before they became dormant in late fall. Plants from the latter two seedings did not form any tillers before they became dormant, but those from the October 28 seeding developed a few tillers over winter. Only 46% and 65% of the fall tillers on plants from the first two dates, respectively, survived the winter, whereas 100% of the fall tillers on plants from the last two dates survived. About 50% to 60% of the surviving fall tillers from the first two dates formed spikes, while approximately 80% of the surviving tillers from the last two dates produced grain.
Plants from the first three seeding dates developed nearly 600 spring tillers per square yard, but plants from the last date formed only 213 spring tillers per square yard (Table 2). About 30% of the spring tillers from the first two dates, 45% of the spring tillers from the third date, and 68% of the spring tillers from the fourth date produced grain. The total number of productive spikes ranged from 260 to 552 per square yard or 1.8 tillers per plant from the last seeding to 3.4 tillers per plant from the first seeding.
Table 2 also lists the yield from the four seeding dates. These dates need to be adjusted for the area in Nebraska to be seeded.