Optimum N fertilization from January until jointing is absolutely essential to profitable wheat production. Research has shown that fall/early winter fertilization is generally very important to early tiller development. Tillers developed in the fall or winter produce greater numbers of wheat kernels per head than tillers developed in the spring. Fall/winter developed tillers also have deeper root systems that give greater protection against dry weather during grain fill in May or early June. Nitrogen timing and rate should be adjusted based on residual nitrogen available to the plant and time of planting. If the crop has already developed 100 or more tillers per square foot with three or more leaves in early February, (this will only happen in timely planted wheat with relatively large amounts of residual nitrogen) the crop does not need additional nitrogen until at least March. When wheat has 50-100 tillers per square foot it is desirable to apply only 30-40 pounds of nitrogen in January/February. Conversely, if wheat has less than 50 tillers per square foot, 40-50 pounds of nitrogen per acre should be applied as soon as possible to stimulate growth and tillering on any winter days when the air temperature averages above 32 degrees. Early February is too early to apply more than 50-60 pounds of nitrogen on most soils. See the figure below for the steps of how to obtain field-specific N rate recommendations for late winter/early spring N applications. A tiller count should be the first step in all fields, regardless of whether spring N applications will be split or not; then follow the arrows. For details of the research and nitrogen recommendations for wheat obtain a copy of Nitrogen Management for Winter Wheat: Principles and Recommendations by Dr. Mark Alley from your local extension agent or on-line at http://www.ext.vt.edu/pubs/grains/424-026/424-026.
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