March 30, 2007

Additions to the March 16 CropWatch Article

An article in the March 16 CropWatch discussed recommendations for applying nitrogen for wheat. Most producers who do not have a soil test will probably not take samples before applying nitrogen. The NebGuide Fertilizing Winter Wheat I: Nitrogen, Potassium, and Micronutrients, (G1460) indicates that if you do not have a soil sample, that you should use a base level of 9 ppm nitrate-N as an average. This may be a suggested level for wheat planted in fallow. For wheat planted after adequately fertilized previous crops, a more accurate level would be 3-5 ppm nitrate-N. Use the table in the March 16 CropWatch article to determine your nitrogen rate.

Another exception would be for wheat planted into last year’s soybean fields. We normally assume a credit following soybean of 45 to 50 lbs nitrogen per acre which should be sufficient for much of our dryland (non-irrigated) wheat. Based on many years of wheat following soybean in plots at North Platte, we found that wheat following soybean needs to receive nitrogen fertilization without the nitrogen credit. Why? Soybean is an excellent scavenger for soil nitrate and residual nitrate levels following soybean are usually in the 2 to 4 ppm nitrate-N range. Nitrogen fixed by soybean does mineralize, but it usually is released too late to benefit the winter wheat crop.

We normally fertilized our wheat (30 to 70 lbs nitrogen per acre) depending on yield for dryland to irrigated cropping systems. If we did not apply nitrogen, we had nitrogen deficient wheat and low yields. When we sampled the wheat stubble for the next crop, we always found elevated nitrate levels, so we reduced nitrogen for the crop following wheat.

Gary W. Hergert
Extension Soils Specialist
Panhandle REC, Scottsbluff