In late January the Nebraska Wheat Board reported declining winter wheat conditions in western and southwestern Nebraska, leading some producers to ask about the potential for reseeding winter wheat. Can areas be seeded or reseeded with winter wheat when field conditions permit? What would be the yield potential?

KSU Wheat Seeding Date Study

Kansas State University researchers conducted a 7-year study (1985-1991) at Garden City, Kansas, where they seeded winter wheat every month from Oct. 1 to April 1. They used a seeding rate of 80 lb/acre of TAM 107.

Grain yields declined progressively the longer planting was delayed after Oct. 1, the optimum planting date for the area (Table 1). Planting dates from Oct. 1 through Jan. 1 provided yields of 50%-100% of full yields. Wheat planted on all dates through March 1 headed and produced grain yields each year. Wheat planted on April 1 did not receive enough cold winter weather to vernalize and so failed each year to head out or produce grain.

With the later planting dates, the grain-filling period was progressively shortened and delayed into warmer weather. This period was hastened by an average of 1.7 days with each monthly delay. The average daily temperature during this grain-filling period increased by an average of 1.5°F per monthly planting delay and became progressively less favorable for plant productivity. Thus, general declines occurred in mature plant height, number of heads per plant, number of kernels per plant, and grain test weight.

Summary

Resulting relative grain yields tapered off with progressive planting dates as follows:

Oct. 1 = 100%


Nov. 1 = 77%


Dec. 1 = 59%


Jan. 1 = 57%


Feb. 1 = 41%

March 1 = 16%

Although wheat yields decline with planting delays, considerable flexibility is available for planting winter wheat.

Vernalization

Winter wheat requires vernalization, a process where plants exposed to cold temperatures experience physiological changes. With wheat this means the plants will not flower until they have been exposed to cold temperatures. Not all plants have a vernalization requirement, and the degree of vernalization required can vary within a species.

Vernalization days (VD) are a measure of cold temperature, similar to how growing degree days (GDD) are a measure of warm temperatures. Contrary to popular belief, the best vernalization temperatures for winter wheat are 40°F – 50°F, not colder temperatures. Vernalization is a biological process and plants have to be biologically active — not frozen — for it to occur.

All winter wheats do not have the same vernalization requirement. Varieties with a higher vernalization requirement need more exposure to cold temperatures.

Estimating late winter or early spring seeding dates in Nebraska that will result in winter wheat being vernalized is difficult because we seldom have an average year. (This all assumes sufficient soil water at seeding.)

In Nebraska we consider 45 days of vernalization to be critical to yield production. Therefore, if you seed by March 1 into moist soil and expect your night temperature to get down to under 45°F for the next 45 days, your winter wheat will vernalize and flower. (Seeding dates will need to be adjusted across the state.)

Recommendations for Reseeding Winter Wheat in Late Winter

• Contact your Farm Service Agency and Crop Insurance Representative before taking any action.
• Select winter wheat varieties with shorter vernalization requirements.
• Increase the seeding rate to 1.5 to 2 times the normal seeding rate.
• Apply starter fertilizer with the seed or close to the seed. (Note: Not all fertilizer is safe to apply with or close to the seed.)
• A disk drill will do less damage to existing winter wheat plants, but does not create much surface roughness.
• Seed at the normal depth (1-2 inches) and as soon as field conditions permit.

While the grain yield from this wheat may not be economical, the residue will benefit future crops and reduce wind and water soil erosion.