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Managing Nitrogen for Yield and Protein in Hard Wheat FS 335 January 2007 M.D. Flowers, L.K. Lutcher, M.K. Corp, and B. Brown Do you want to print a copy? We recommend downloading the print version (192 KB). First download the free Adobe Reader, if you don't already have it. Contents Principles of nitrogen management for hard wheat production Calculating a nitrogen application rate The successful production of hard wheat with acceptable protein is based, in part, on an effective nitrogen (N) management plan. This fact sheet discusses the principles of managing N for hard wheat production and explains how to calculate an N application rate. The information contained in this fact sheet is applicable to both irrigated and dryland production systems in eastern Oregon. top Principles of nitrogen management for hard wheat production Table 1.—Wheat class and corresponding protein goals. Wheat class Protein goal (%) Hard red winter (HRW) 12.5 Hard white winter (HWW) 12.5 Hard red spring (HRS) 14 Hard white spring (HWS) 12.5 Grain protein goals differ among hard wheat classes (Table 1). Maximum N uptake in wheat occurs after tillering and before flowering (Figure 1). Nitrogen accumulated during these growth stages is used primarily to establish yield potential. Nitrogen accumulated after flowering has little effect on yield but can increase grain protein content under favorable conditions. Nitrogen requirements for high protein hard wheat are greater than those for low-protein soft wheat. The extra protein in hard wheat accumulates in grain when plant uptake of N exceeds that required for yield (Figure 2). Nitrogen requirements for desired grain protein goals are listed in Table 2. Moisture availability throughout the growing season influences both grain yield and protein content. Under favorable moisture conditions, yield potential increases and “dilutes” the amount of protein in the developing wheat kernels. Supplying additional N to compensate for the higher yield potential may be necessary to attain targeted protein contents. Conversely, under limited moisture conditions, yield potential decreases and grain protein may increase because N is concentrated in fewer wheat kernels. Figure 1.—Wheat nitrogen (N) uptake during the growing season. Table 2.—Nitrogen (N) required (per bushel of wheat) to reach a specific grainprotein goal. Grain protein goal % N requirement Average (lb N/bu) Range (lb N/bu) 10 2.4 2.2–2.6 11 2.7 2.4–2.9 12 3.0 2.6–3.2 13 3.3 2.8–3.5 14 3.5 3.0–3.7 15 3.7 3.3–4.0 Nitrogen fertilizer may be applied in split applications, depending on the production system and moisture conditions during the growing season. In irrigated cropping systems, N may be applied as required by the crop. Dryland growers should apply most of the N fertilizer prior to or during seeding. Early-spring (prior to jointing) applications may be necessary if fall, winter, or spring moisture is greater than expected and yield potential has increased beyond the N supply. Account for residual soil N when determining the amount of N required to achieve grain yield and protein goals. The results from a flag leaf tissue test can be a useful indicator of grain protein content in some hard wheat classes. Take flag leaf samples at 50 percent heading (Feekes 10.3). Grain protein is unlikely to increase in hard spring wheat if the flag leaf N concentration exceeds 4.2 percent. If the flag leaf N concentration is below 4.2 percent, a late-season N application may increase grain protein. Late-season N applications are untested under dryland conditions, and their effectiveness for raising grain protein is unknown. Sulfur is an important component of grain protein and often is a limiting nutrient in hard wheat production. The sulfur requirement is approximately one-tenth of the nitrogen requirement. Applications of up to 25 lb S/acre are common in hard wheat production. Figure 2.—Generalized relationship between grain yield, grain protein, and nitrogen (N) supply. top Calculating a nitrogen application rate Step 1. Determine the total amount of N required to reach the desired yield and protein goal. Use past production history to set realistic yield goals for each field. Generally, hard winter wheat yields are equal to or slightly (10 percent) lower than those for soft white winter wheat. Using the appropriate protein target from Table 1, determine the amount of N required per bushel of wheat using Table 2. Keep in mind the following when determining the amount of N required per bushel of wheat. Highly productive systems require less N per bushel than low productivity systems. For example, irrigated systems require less N per bushel than less productive dryland systems. In general, hard wheat requires an additional 0.4 lb N/bushel compared to that required for maximizing yield. Calculate the total amount of N required by the crop by multiplying the yield goal (bushels of wheat per acre) by the pounds of N required per bushel. This is the total amount of N required per acre. Step 2. Determine the amount of residual soil N. Collect a representative soil sample from the effective crop root zone in 1-foot increments and send to a laboratory for analysis of plant available nitrogen. The surface sample (0–1 foot) should be analyzed for nitrate N (NO3-) and ammonium N (NH4-N). The remaining samples should be analyzed for NO3- only. Add reported values for all depths to determine the amount of residual soil N. Step 3. Determine the amount of N fertilizer required. Subtract the residual soil N (Step 2) from the total N requirement (Step 1) to obtain the amount of N fertilizer required. Example: Nitrogen (N) application rate calculation for hard red winter wheat. Step 1. Determine the total amount of N required (per acre). Yield goal = 60 bu/acre HRW protein goal (Table 1) = 12.5% Nitrogen required per bushel of wheat to reach protein goal (Table 2) = 2.6–3.5 lb N/acre; average = 3.1 lb N/acre Total N required per acre = yield goal x N required per bushel Total N required: 60 bu/a x 3.1 lb N/a = 186 lb N/a Step 2. Determine residual soil N. Depth (feet) Soil NO3-N (lb/acre) Soil NH4+N (lb/acre) Total N (lb/acre) 0-1 15 10 25 1-2 15 - 15 2-3 10 - 10 Total 40 10 50 Soil residual N: 50 lb N/a Step 3: Determine N fertilizer rate. N fertilizer rate = Step 1 - Step 2 N fertilizer rate: 186 lb N/a - 50 lb N/a = 136 lb N/a For more information Many OSU Extension Service publications may be viewed or downloaded from the Web. Visit the online Publications and Multimedia catalog at http://extension.oregonstate.edu/catalog/ Copies of our publications and videos also are available from OSU Extension and Experiment Station Communications. For prices and ordering information, visit our online catalog or contact us by fax (541-737-0817), e-mail (puborders@oregonstate.edu), or phone (541-737-2513). Nitrogen Management for Hard Wheat Protein Enhancement, PNW 578 (2005). Winter Wheat in Summer-Fallow Systems (Low Precipitation Zone), FG 80 (revised 2006). Winter Wheat and Spring Grains in Continuous Cropping Systems (Low Precipitation Zone), FG 81 (revised 2006). Winter Wheat in Summer-Fallow Systems (Intermediate Precipitation Zone), FG 82 (revised 2006). Winter Wheat in Continuous Cropping Systems (Intermediate Precipitation Zone), FG 83 (revised 2006). Winter Wheat in Continuous Cropping Systems (High Precipitation Zone), FG 84 (revised 2006) Prepared by Michael D. Flowers, Extension cereals specialist; Larry K. Lutcher, Extension faculty (crops), Morrow County; Mary K. Corp, Extension faculty (cereals), Umatilla County (all of Oregon State University); and Brad Brown, Extension soil and crop management specialist (University of Idaho). Published January 2007.

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