April 10, 2009

Figure 1. Seven-day average soil temperature at 4-inch depth, April 4-April 10.

Because of our cool spring (Figure 1), there is still time to check soil moisture, assess wheat stands, and evaluate your marketing plan to determine if additional nitrogen is needed for this year's winter wheat crop.

Wheat prices have declined significantly since last year while fertilizer prices rose. Fertilizer prices were very high last fall but are decreasing. If you didn't buy N fertilizer last fall or early winter, you can still buy lower cost N and apply it before wheat reaches the jointing stage.

Spring Nitrogen Management

Nitrogen rates should be based on soil tests for residual nitrate to a three-foot depth. If you do not have a soil sample, use a base level of 6 to 8 ppm nitrate-N for wheat planted after fallow and 4 ppm for wheat planted after an adequately fertilized previous crop (shaded area in Table 1). Table 1 shows recommended rates at $0.60 per pound of nitrogen for different wheat prices.

For irrigated wheat, current guidelines suggest adding 1.5 pounds of N per bushel above a 75 bu/ac yield level if you have consistently produced above that level. A web-based Excel worksheet for calculating recommended nitrogen is at http://soilfertility.unl.edu.

Nitrogen Solutions

Determining your viable stand is equally important for weed control decisions and may influence your N fertilization. If nitrogen solution-herbicide combinations are used, they need to be applied early for many broadleaf weeds. An early N application allows more time for distribution into the root zone, but a herbicide application may be too early to control some weeds. Later applications may be optimum for some weeds but may cause problems with plant injury because of the herbicide-fertilizer combination.

Urea

Urea (46-0-0) is a good choice for spring topdressing if applied early. The cooler temperatures and the higher probability of precipitation help assure a lower potential for N volatilization loss. Several products can reduce N volatilization (see March 27 CropWatch for Tips for Maximizing Nitrogen Efficiency).

Gary W. Hergert
Extension Soils Specialist, Panhandle REC