April 1, 2011

Wheat stands in much of Nebraska’s wheat growing area are spotty or at below normal condition, largely due to limited moisture last fall and winter. (See related story.) Given these conditions, you may be evaluating your stand, weighing the high price of fertilizer with the high price for wheat, and trying to decide whether to fertilize your wheat this spring.

If you did not book your fertilizer supplies earlier, you will pay a premium this spring. However, many less than desirable stands may produce a profit if weeds can be controlled.

Available Nitrogen

The lack of moisture this winter should have limited any loss of N due to leaching or denitrification. The N you applied last summer and/or fall is still there just waiting for the crop to begin growing.

To decide whether to add N this spring, use Table 1. The N price is set at $0.60 which is in the range of current N prices for urea or UAN solution. Nitrogen rates should be based on soil tests for residual nitrate to a three-foot depth. If you don’t have a soil sample, use a base level of 6 ppm nitrate-N for wheat planted after fallow and 4 ppm for wheat planted after an adequately fertilized previous crop (shaded area). With drier, cooler conditions this spring, there should be plenty of time to apply N before wheat reaches the jointing stage.

See EC 143 for N recommendation tables or use the simple winter wheat fertilizer calculator (an Excel® spreadsheet) on the CropWatch Wheat page.

The dilemma for producers this year is what to do with a spotty stand (Figure 2). If you assume you have 20% bare area, should you only use 80% of the rates in Table 1? Probably not. The wheat that is growing well and has good yield potential still needs adequate N to reach its maximum yield potential.

Applying 80% of the normal rate to both healthy and spotty areas means you’ll be applying fertilizer on areas that won’t grow anything or will have lower production. Some N will move from the areas with no crop, but wheat roots only expand laterally about 2 feet from the plant.

That’s why evaluating your stand is essential to determining how you manage weed control and N fertilization. With 50 lb of N at $0.60 and $6 wheat, you will need a 5 bu/ac yield increase just to pay for the fertilizer. Yield increases for wheat with low soil nitrate should be in the 10 to 12 bu/acre range.

N Sources

Applying N to dry, cool soils reduces the potential for N volatilization losses from urea-based fertilizer (urea and UAN solution). If N must be applied to moist soils, consider using a urease inhibitor.

Potential N losses (usually less than 10-15 %) must be weighed against the additional cost of the inhibitor.

Gary Hergert, Extension Soils Specialist
Panhandle Research and Extension Center, Scottsbluff