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Managing nitrogen fertilizer applicationBy Randy Buhler CSU Cooperative Extension Agent, agronomy, Logan County Colorado Several weeks ago this column discussed assessing wheat stands for yield potential. This week's column provides information about using the yield potential assessment to manage your nitrogen fertilizer application. A realistic yield goal is the first consideration for deciding nitrogen fertilizer requirement. Our fields need nitrogen application to produce economic yields. Soil testing is the best way to determine carry-over nitrogen. Manure or compost applications made just before planting will not provide sufficient nitrogen to meet the wheat crop's needs. Be sure to credit fall nitrogen applications and N in starter fertilizer you applied at planting. Soil mineralization is very slow during the winter months because of low temperatures. The mineralization rate is slow in dry soils. Research in Kansas showed a loss of N from single N applications made before the spring green-up. This can result in yield reduction of up to 19 percent compared to a properly timed application. The appropriate timing is between green-up and early stem elongation (before second visible node). Stem elongation (jointing) is also the time to remove grazing animals from fall planted wheat. Dry granular urea and urea-ammonium nitrate solutions are the most likely sources of N this spring season. Dry urea has the least potential of causing damage to the foliage. UAN generally causes insignificant browning of foliage when applied early. Adding herbicide to the fertilizer solution is a common practice. Late applications of UAN can cause severe leaf burn. Dribble-band application can reduce this injury, but excludes adding herbicide. For irrigated wheat, the nitrogen rates are higher than for dryland wheat. Apply your N requirement by injecting UAN through the sprinkler. You must have properly constructed injection plumbing with back-flow preventer to be safe. You must also have a chemigation license from the Colorado Department of Agriculture to be legal. Another aspect of N fertilization is protein content of the grain at harvest. To move the protein content one percentage point above 12 percent requires 20 to 30 pounds of N per acre. Unless the market prices higher protein content equivalent to the cost of nitrogen to produce that protein, it makes little sense to fertilize for greater than 11 to 12 percent protein content. At harvest time, you can rate your success with N management by measuring the grain protein. Protein between 11 and 12 percent indicate a good job on N management. Grain protein above 12 percent indicates you have fully met the crops N requirement for this season. Protein below 11 percent indicates inadequate N fertilization was available to the crop. Severe drought can skew these indicators, as will hail, insect, and disease damage. 3/17/08 Date: 3/12/08
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