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Agronomic Crops Network

Ohio State University Extension



A successful soil fertility program for wheat requires knowledge of a field’s yield potential and a recent soil test. The soil test will provide current levels of phosphorus and potassium in the soil and the soil pH. Soil pH will assist in determining the need for micronutrients and other soil amendments most importantly lime. When the proper soil pH is maintained, adequate levels of micronutrients and secondary nutrients should be released by the soil organic matter. The proper soil pH for western Ohio (subsoils de- rived from limestone) should be above 6.0 and below 7.0, and above 6.5 and below 7.0 for eastern Ohio (subsoils derived from shale and sandstone). The lime test index or buffer pH on the soil test should be used for lime recommendations. These recommendations are for mineral soils with adequate drainage containing 1 to 5 percent organic matter. Organic soils (organic matter > 20 percent) and sandy soils (CEC < 6) will require different recommendations. 

The Ohio State University currently uses the Extension Bulletin E-2567, Tri-State Fertilizer Recommendations
for Corn, Soybean, Wheat, and Alfalfa 
( for nitrogen, phosphorus and potassium recommendations. The following discussion of these nutrients have been adapted from this publication. 

Nitrogen (N) 

Nitrogen rates are based on yield potential and not on soil analysis. Total nitrogen recommendations are given in Table 1 or may be calculated by the following equation: 

40 + [1.75 x (yield potential – 50)] 

For the corresponding rate, part of it should be applied in the fall and the rest after green-up. Generally, 20 to
30 pounds of fall applied nitrogen should be adequate for early fall and spring growth. Spring recommendations should be the total nitrogen required less the amount applied in the fall. No credits are given for previous crops. For example, a wheat crop with a 90-bushel-per-acre yield goal would require 110 pounds nitrogen per acre (Table 6-5). If the grower applied 20 pounds in the fall, the remaining 90 pounds should be applied in the spring. 

Table 6-5: Nitrogen Recommendations for Wheat. 

Yield Potential (bu/ac)  Nitrogen Rate (lb/ac) 
60 60
70 75
80 90
90 110
100 130

Yields are generally not affected when the initial spring nitrogen is applied between green-up and Feekes GS (Growth Stage) 6 (early stem elongation). Nitrogen losses may be severe on applications prior to green-up and may cause significant yield reductions, regardless of nitrogen source. Significant yield losses may also occur if initial spring applications are delayed until after Feekes GS 6. 

Split Applications and Nitrogen Source. Split application may improve nitrogen efficiency; however, in most years, yield gains from a split application have not been large enough to offset the application cost of a second trip across a field. A split spring application program may be a benefit in poorly drained fields that are prone to nitrogen loss, and also in years that the potential for nitrogen loss is great. Years that have a potential for nitrogen loss generally have a warmer than normal winter followed by a warm and wet April. Delaying initial nitrogen application until closer to Feekes GS 6 would have the same effect as a split application without sacrificing yields. In a split application program, the larger proportion of the nitrogen should be in the second application by Feekes GS 6. 

Nitrogen Source. Nitrogen source is not a concern unless conditions are conducive for nitrogen loss. In general, urea-ammonium nitrate solutions have the greatest potential for loss, then urea, and ammonium sulfate the least. Risk for nitrogen loss potential is the greatest for early applications and decreases as plants approach Feekes GS 6. Fields prone to wet conditions would also be susceptible to nitrogen loss. If nitrogen loss is not a concern, economics and application equipment should determine nitrogen source. 

Nitrogen Summary. Initial spring application should be applied between green-up and Feekes GS 6. Waiting until Feekes GS 6 may increase yields slightly but the small gain is offset by the risk of an extended wet period at elongation time. If these wet conditions delay application until late stem elongation or later, a yield decrease may occur. Nitrogen source should be dependent upon the risk of nitrogen loss conditions and cost. 

Phosphorus (P) 

Phosphorus should be applied before planting when the soil-test level is below 50 ppm. Recommendations are determined by yield goal and soil-test level (Table 6-5). Phosphorus and fall-applied nitrogen are often applied as diammonium phosphate (DAP) or monoammonium phosphate (MAP). 

Table 6-5: Phosphorus Recommendations for Wheat at Various Yield Potentials and Soil-Test Levels

Yield Potential (bu/ac) Soil-Test P (Bray) in ppm
  15 20 25-40  45 50
  lb P2O5/acre
60 90 65 40 20 0
70 95 70 45 20 0
80 100 75 50 25 0
90 105 80 55 30 0
100 115 90 65 30 0

Potassium (K) 

Potassium recommendations are based upon yield goal, soil CEC and the soil- test level (Tables 6-6 and 6-7). Soils with larger CEC values have a greater chance of potassium becoming unavailable to the crop, and require more potash than low CEC soils. Table 6-6 recommendations only account for grain removal of potassium by the crop. Recommendations should be greater in fields where the straw may be baled and removed (Table 6-7). 

Table 6-6: Potash Recommendations for Wheat at Various Yield Potentials, CECs and Soil-Test Levels―Only Grain Removed (no straw removal). 

Yield Potential Soil (bu/ac) CEC  Potential Soil (bu/ac) CEC  Soil-Test K (ppm) 75 100 125 
    25 50 75 100 125 150 175
60   lb K2O/acre 
  10 155 115 80 40 40 0 0
  15 195 150 110 65 40 25 0
  20 240 190 140 90 40 40 0
80   lb K2O/acre 
  10 160 125 85 50 50 0 0
  15 205 160 115 70 50 30 0
  20 250 200 150 100 50 50 0
100   lb K2O/acre 
  10 170 130 95 55 55 0 0
  15 210 165 125 80 55 35 0
  20 260 205 155 105 55 55 0

Table 6-7: Potash Recommendations for Wheat at Various Yield Potentials, CEC and Soil Test Levels―Both Grain and Straw Removed. 

Yield Potential

Soil CEC Soil-Test K (ppm)            
(bu/ac)     25 50 75 100 125 150 175


  lb K2O/acre 
  10 210 170 135 100 100 0 0
  15 250 205 160 120 100 60 0
  20 300 250 200 150 100 100 0
80   lb K2O/acre 
  10 235 200 160 120 120 0 0
  15 275 230 190 145 120 80 0
  20 320 270 220 170 120 120 0
100   lb K2O/acre 
  10 260 225 185 150 150 0 0
  15 300 260 215 170 150 95 0
  20 350 300 250 200 150 150 0

Sulfur (S) 

Sandy soils and soils low in organic matter often respond to sulfur fertilizer. Medium- to fine-textured soils with adequate organic matter generally have not produced larger yields with supplemental sulfur. Current research has shown no yield increase on these soils. However, atmospheric depositions have decreased over past decades as sulfur emissions from manufacturing processes have diminished, which may cause these soils to be deficient in the future. Sulfur rates have not been established as a result of soils generally not being deficient; however, 20 to 40 pounds per acre of sulfur mixed with topdress nitrogen should be adequate for soils suspected of being deficient. Suitable sulfur fertilizers include: ammonium sulfate, ammonium thiosulfate and gypsum. 

Manganese (Mn) 

Manganese (Mn) deficiency has rarely been seen in Ohio wheat fields. Generally, the whole field is not deficient, and the deficiency is found in pockets and small areas of a given field. Deficient soils have generally occurred where soil pH is above 7.0. Deficient plants will have reduced tillers, appear weak and thin, and have leaves with interveinal chlorosis or white specks and blotches. Foliar applications of 4 pounds per acre of manganese (generally manganese sulfate) is often the best practice for mineral soils with a history of manganese deficiency, which may be added to spring applications of urea-ammonium nitrate.