August 30, 2012

The drought this year may have wheat producers questioning fertilizer application. Most soils in western Nebraska have a powdery dry (tilled) or baked dry (no-till) surface (see Figure 1). In many fields there are 3 to 5 inches of loose dry soil on the surface (Figure 2). Many fallow fields have lower than average stored soil moisture.

Some producers are considering planting longer coleoptile varieties using hoe drills with 12- to 14-inch spacing to reach moisture. Producers using wheat varieties with shorter coleoptile lengths have two options: plant into dry soil and wait for rain or wait for rain and plant later. The problem with the drought is, how long should you wait? Long-range weather conditions suggest dry conditions until November which is too late for planting. With all these uncertainties, what are the options for fertilization?

One option is to do nothing and wait. The primary concern is low to medium soil levels of phosphorus. Inadequate phosphorus will hinder normal root development and limit yield potential to N. Hopefully, you took soil tests earlier this summer. Those results can provide assurance about current phosphorus levels and help you decide whether you can play the waiting game.

If soil test levels for P were low, the best option now is to use at-planting, row-applied liquid or dry N-P fertilizer (10-34-0 liquid, 11-52-0 or 18-46-0 dry). P can be broadcast if there is time for light incorporation before planting. In most cases it will not dry the soil out any more, however a trip across the field is another expense. Not mixing will leave the P mostly on the surface where it will do little good for the next crop.

Applying phosphate is profitable. Nebraska data shows up to 20 bu/ac increases when P is applied at low soil test levels and up to 10 bu/ac when it’s applied in medium P soils at normal dryland yield levels. The most profitable P rate depends on

• the P source used,
• wheat and fertilizer prices,
• soil pH and
• the method of application.

Row or dual-applied P is a more efficient method of P application than broadcast and may be the best strategy during uncertain times.

For nitrogen, many producers who apply anhydrous ammonia held off due to higher prices late this spring and the concern for drying out the soil even more. Wheat does not require much N for fall growth. If the residual soil nitrate level is 6 ppm or above in the top foot, you can probably wait to see how the crop emerges and survives the winter. Depending on yield potential, an early spring topdress can still produce a good yield and adequate protein. Depending on soil nitrate level, yield potential, and wheat and fertilizer price, N application could be from 20 to 80 lb per acre. (See the UNL publication, Fertilizing Winter Wheat (EC143), for N recommendations based on soil nitrate, fertilizer N, and wheat price.)

Knife (dual) placement of P and seed-applied P perform equally at optimum seeding dates. If the seeding date is delayed or growing conditions prevent or delay root growth to the dual placement band, then seed placement is the preferred application method. Dual placed P can be readily applied with standard ammonia applicators equipped to dispense 10-34-0. The normal ammonia application depth (4 to 6 inches) is also optimum for P. Knife spacing should be no greater than 15 inches.

Gary Hergert
Extension Soils Specialist