Figure 1. Wheat seeded into skip-row corn fallow in western Nebraska. Notice the value of residue to provide an improved stand. This field was hailed three times and while residue was severely limited, it greatly improved the stand and seeding conditions.  The wheat yield was over 70 bu/ac.

August 24, 2012

At the UNL Dryland Farm south of North Platte this has been the driest period (Sept. 1, 2011 - Aug. 21, 2012) since record-keeping began in 1907 with 10.79 inches of precipitation. The same period in 2002 was the second driest with 10.81 inches of precipitation. The driest crop season also was this year. From May 1 - August 21 we had 2.66 inches of precipitation. In 2002 we had 3.93 inches.

The average high temperature of 70.46°F for January 1 to August 21, 2012 ranked second highest since 1907. The high of 71.73°F was recorded in 1934. With conditions like these going into wheat planting season, many producers are weighing the risks and wondering whether it's better to seed winter wheat now or wait for rainfall to improve soil moisture.

For tilled seedbeds (usually fallow) where the seed can be placed in firm soil at the correct seeding depth for the winter wheat variety, the crop producer's best option is probably to go ahead and seed even if the soil is dry and the wheat seed will not germinate immediately. Wheat requires 41% seed moisture for germination, which is 9% more than corn (32%) but 10% less than soybean (51%).

The maximum depth a winter wheat variety with a short length coleoptile can be seeded is 2 inches in a silt loam soil. In extremely fine-textured soil with a high clay content, reduce seeding depth by 0.5 inch. In coarse-textured soils with lots of sand, increase seeding depth by 0.5 inch. For winter wheat varieties with medium length coleoptiles these seeding depths can be increased by 0.5 inch; for varieties with long coleoptiles, seeding depth can be up to 3 inches with the adjustment for the soil texture. Warmer soil tends to shorten the coleoptile length. The coleoptile penetrates the soil and results in seedling emergence. If the seed is planted too deep, beyond the elongation of the coleoptile, seedlings cannot emerge and the result will be a poor stand.

If the seedbed is loose and the seed would be placed in loose soil, delay seeding until there is moisture to firm the seedbed. Seed placed in a loose seedbed is one of the leading causes of winter injury such as winterkill and root and crown rot.

Before beginning to seed, make sure opener disks on the drill are not worn. For hoe drills, good quality spear point or eagle beak openers usually improve performance. Hoe drills, especially those with wider row spacing, are able to place the seed deeper because they can build a ridge and plant in the furrow. Use a slower ground speed so adjacent rows are not covered with soil. The seeding depth then becomes the soil cover over the seed, not the operating depth of the opener. If the seedbed was not tilled too deep, it usually is possible with the hoe drill to place the seed in firm, moist soil. Deep tillage or applying anhydrous ammonia with knives can dry out the soil, so it could be impossible to place the seed in firm, moist soil even with a hoe drill.

As with everything, there are drawbacks to the hoe drill. The biggest is that if a hard rain occurs, the ridges will be destroyed and the seed, or developing plant, will end up under too much soil cover. In addition, the hoe drill does considerable tillage, burying residue which is best left on the soil surface to conserve moisture.

Seeding with a disc drill in a loose seedbed almost guarantees disaster unless it rains immediately after seeding. Leveling the drill slightly tail down, rather than running it level, will improve seed-to-soil contact by putting more pressure on the press wheels. However, it is difficult to firm dry soil around the seed and seeding should probably be delayed until there is moisture.

For continuous cropping, do not till. If you do till, the seedbed will dry out to the depth of tillage. The soil should be firm after soybeans are harvested and tillage is not needed as wheat prefers a firm seedbed.

When seeding winter wheat this year, make sure the drill is running lower in back than normal. Transfer more drill weight to the back of the drill and add extra weight to the drill. This will allow for penetration into dry, hard soil, forcing the seed into the soil and insuring seed-to-soil contact. Also, don't seed wheat too shallow. When using disc drills, plant at a depth of 2 inches or more.

Do not seed winter wheat much earlier than the suggested seeding date for your area. Early seeding leads to problems with diseases such as wheat streak mosaic and insects such as the Hessian fly. See the article in this week’s CropWatch on suggested seeding dates and how to compensate for late seeding.

As with all these rules there are exceptions. The biggest is to make sure you seed by the required date for crop insurance in your area (see box).

Robert Klein
Extension Crops Specialist
West Central REC
Paul Jasa
Extension Ag Engineer
P. Stephen Baenziger
Professor of Plant Breeding