Recommendations in this fertilizer guide apply to tillage fallow-winter wheat and chemical fallow-winter wheat cropping systems. This guide is one of a set of publications that address the nutritional requirements of nonirrigated cereal crops in north-central and Eastern Oregon (Table 1).
Nitrogen
Calculate nitrogen (N) application rates by subtracting soil test nitrogen from crop demand for nitrogen. Adjust for excessive straw and/or soil sampling in the spring of the summer-fallow year. Evaluate application rates by reviewing the protein content of harvested grain. A detailed explanation is provided below.
Crop demand for nitrogen
Multiply expected yield by the nitrogen requirement to get crop demand for nitrogen. The nitrogen requirement, which is the amount of nitrogen required to produce 1 bushel of wheat, is based on a grain protein goal (Table 2).
A grain protein content of 10% is optimum for soft white wheat. Desired grain protein concentrations for hard wheat range from 11%–13%. 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 nitrogen exceeds that required for maximum yield (Figure 1).
Table 1. Fertilizer guides for nonirrigated cereal production in Oregon
Low precipitation zones (less than 12 inches)
- Fertilizer guide for winter wheat in summer-fallow systems in low precipitation zones, FG 80
- Fertilizer guide for winter wheat and spring grains in continuous cropping systems, FG 81
Intermediate zones (12–18 inches)
- Fertilizer guide for winter wheat in summer-fallow systems in intermediate precipitation zones, FG 82
- Fertilizer guide for winter wheat in continuous cropping systems in intermediate precipitation zones, FG 83
High precipitation zones (more than 18 inches)
|
Grain protein goal |
|
|
|---|---|---|
|
(%) |
Average (lb N/bu) |
Range (lb N/bu) |
| 9 | 2.2 | 2.0–2.4 |
| 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 |
Subtract soil test nitrogen
Laboratory methods are used to test soil samples for plant-available nitrogen (soil test nitrogen). Collect samples from the effective root zone (usually 4 feet) in 1-foot increments and have them analyzed for nitrate nitrogen (NO3-N). Samples from the surface foot also should be analyzed for ammonium nitrogen (NH4-N). Add reported values for all depths to get total soil test nitrogen (Table 3).
Periodic assessment of nitrate concentration in the fifth and sixth foot can be used to fine-tune nitrogen management. If nitrate concentrations are high or increase over time, consider adjusting the application rate or the time of application. Split applications may improve nitrogen use efficiency.
|
Soil depth (inches) |
Ammonium nitrogen (NH4-N) (lb/acre) |
Nitrate nitrogen (NO3-N) (lb/acre) |
Total soil test nitrogen (NH4-N + NO3-N) (lb/acre) |
Amount to subtract (lb/acre) |
|---|---|---|---|---|
|
0–12 |
5 | 15 | 20 | 20 |
|
13–24 |
— | 15 | 15 | 15 |
|
25–36 |
— | 10 | 10 | 10 |
|
37–48 |
— | 5 | 5 | 5 |
|
Profile* |
5 | 45 | 50 | 50 |
|
49–60** |
— | 12 | 12 | — |
|
61–72** |
— | 10 | 10 | — |
* Calculation of the nitrogen application rate should be based on soil test results from the top 4 feet or the effective root zone.
** Nitrogen in the fifth and sixth foot usually does not contribute to yield but may increase grain protein.
Adjust for excessive straw
Nitrogen “tie-up” in crop residue (immobilization) temporarily reduces the amount of available nitrogen in the soil; immobilization can be a problem when greater-than-average quantities of straw are present in the field.
Grain yield can be used to estimate the quantity of straw. Straw loads increase by about 100 lb/acre for each bushel increase in yield. Adjust the calculated nitrogen application rate as shown in Table 4 if grain yield from the previous wheat crop exceeded the long-term field average by 10 bu/acre or more.
Adjust for soil sampling (spring of the summer-fallow year)
Decrease the calculated application rate by 10 to 20 lb N/acre if fields are sampled in the spring of the summer-fallow year. This adjustment will compensate for mineralization. Mineralization is a biological process that increases the supply of available nitrogen in the soil; it is favored by moist or wet soils and warm temperatures.
Mineralization may increase the supply of available nitrogen by more than 10 or 20 lb/acre when average or above-average precipitation follows a prolonged drought. Adjustment of the nitrogen application rate is not necessary if fields are sampled within six weeks of fall seeding.
Review protein content
of harvested grain
A postharvest review of grain protein can be a good way to evaluate application rates. Higher-than-desired protein indicates overfertilization — if growing conditions were normal or about average. High protein also can be caused by unusually dry conditions or nitrogen that is positioned deep in the soil profile.
Lower-than-desired protein may be due to an insufficient application rate. Low protein also can be a problem when late-season rainfall results in above-average yield or when nitrogen losses occur during or after application. Examples of nitrogen losses include “escape” of anhydrous ammonia from dry soil or an unsealed soil surface, volatilization of surface-applied urea and nitrate leaching below the root zone.
|
Greater-than-average wheat yield (previous crop) (bu/acre) |
Corresponding increase in straw production (lb/acre) |
Increase application rate by (lb N/acre) |
|---|---|---|
| +10 | 1,000 | 10 |
| +20 | 2,000 | 20 |
| +30 | 3,000 | 30 |
Phosphorus
Application of phosphorus (P) should increase yield if soil test levels are less than 10 ppm (Table 5). A phosphorus application is not recommended when soil test values are greater than 15 ppm.
Phosphorus response in fields with soil test values of 11 to 15 ppm is highly variable. Yield increases from fertilization seem to be associated with: (1) high yield potentials, (2) late seeding dates, or (3) root diseases that limit plant growth and development.
Optimum efficiency is achieved by banding phosphorus. Placement of either liquid or dry material with the seed, below the seed, or below and to the side of seed is recommended. Subsurface shank applications also are effective. Broadcast applications are not recommended.
|
Soil test phosphorus (P) (ppm)* |
Plant-available index |
Amount of phosphate (P2O5to apply (lb/acre)** |
|---|---|---|
| 0–5 | Very low | 10–15 |
| 6–10 | Low | 5–10 |
| 11–15*** | Moderate | 0–5 |
| Over 15 | High | 0 |
* Plant-available index is correlated to sodium bicarbonate-extractable phosphorus only and does not apply to other test methods.
** Recommended application rates apply to banded or subsurface shank applications.
*** Phosphorus response in fields with soil test values between 11 and 15 ppm is highly variable.
Potassium
Soil potassium (K) concentrations in the region generally are high or very high (>100 ppm extractable K). Fertilizer applications are not recommended.
Sulfur
Sulfur (S) is one of the most limiting nutrients for wheat production — second only to nitrogen in importance. The sulfur requirement of the wheat plant is about one-tenth the nitrogen requirement. Sulfur is necessary for optimum yield and high-quality baking flour.
Sulfur deficiencies in wheat are fairly common in the spring after a wet winter. Above-average precipitation moves sulfate-sulfur (SO4-S), the form of sulfur available to plants, below the root zone. Deficiency symptoms often disappear later in the season as root growth extends to deeper layers of the soil profile.
The soil sulfur (SO4-S) test is not definitive. Low or moderate soil test levels (Table 6) are a first indication that fertilization might be warranted. Other factors need to be considered. Yield responses are more likely if one or more of the following situations apply: (1) winter wheat is seeded late in the fall, (2) more than five years have passed since the last application of sulfur, and/or (3) greater-than-average quantities of straw are present in the field. Field experience, observation and on-farm experimentation provide valuable information about the need for sulfur.
|
Soil test sulfate-sulfur (SO4-S) (ppm) |
Plant-available index |
Amount of sulfur (S) to apply (lb/acre)* |
|---|---|---|
| 0–5 | Low | 5–10 |
| 6–10 | Moderate | 0–5 |
| Over 10 | High | 0 |
*A decision to apply sulfur should not be based on soil test results alone. Sulfur may be beneficial if SO4-S soil test values are low or moderate and if: (1) winter wheat is seeded late in the fall, (2) more than 5 years have passed since the last application of sulfur, and/or (3) greater-than-average quantities of straw are present in the field.
Optimum efficiency is achieved by banding sulfur. Placement of either liquid or dry material with the seed, below the seed, or below and to the side of seed is recommended. Subsurface shank applications also are effective.
Ammonium thiosulfate liquid (Thiosul, 12-0-0-26) is an effective source of sulfur, but it can injure or kill seedlings when placed with the seed. Avoid this problem by placing the product below or below and to the side of seed.
Elemental sulfur should be used with caution because it is not immediately plant-available. Microorganisms oxidize elemental sulfur to plant-available sulfate, but conversion occurs slowly and is regulated by the moisture status and temperature of the soil. Most of the elemental sulfur will not be available until two or three years after application. Rates of 100 lb elemental S/acre may be necessary to ensure that adequate sulfate is available during the first growing season.
Boron
Applying boron (B) fertilizer may improve yield by 1 to 3 bu/acre if the surface-foot DTPA-Sorbitol soil test level is less than 0.5 ppm. The probability of a response increases when the level drops to 0.3 ppm and yield potential is greater than 50 bu/acre.
Application of boron with the seed is not recommended. Foliar applications of boron can be helpful. Foliar rates are much lower than rates applied to soil, so repeat applications in following years may be necessary.
Calibration of application equipment is crucial because the range between an agronomically appropriate rate and a "toxic" application is narrow. Limit first-time applications of boron to small acreages.
Chloride
Research shows that application of chloride (Cl) may increase grain yield, test weight and/or kernel size. It is important to note, however, that these responses occur only some of the time.
Chloride applications are known to increase yield of winter wheat suffering from “take-all” root rot, and they reduce the severity of physiological leaf spot. Yield responses in the absence of disease also have been observed and may be a consequence of improved plant-water relations.
Consider applying chloride if soil test concentrations in the surface foot are less than 10 ppm. The recommended application rate for chloride is 10 to 30 lb/acre. Benefits from fertilization may last for several years.
Yield increases, when they occur, usually range from 2 to 5 bu/acre. Responses are most often associated with above-average yield. Growers are advised to experiment with chloride on small acreages.
Do not apply chloride with the seed; it is a soluble salt that can delay germination or injure or kill germinating seeds. Rain is required after application to move surface-broadcast chloride into the root zone.
Potassium chloride (KCl) is the most readily available source of chloride.
Copper
Soil test levels of copper (Cu) are usually two to three times greater than the established critical level for winter wheat. A nutritional response to the application of copper would be extremely rare. Copper fertilization of dryland wheat (in Oregon) has not been beneficial in research trials.
Zinc
Soil test zinc (Zn) levels have been declining over time. Zinc application could increase yield by 2 to 3 bu/acre if the surface-foot DTPA extractable soil test level is less than 0.3 ppm.
The potential for a grain yield response increases when soil phosphorus levels are high, the soil pH is greater than 7.0, and yield potential exceeds 50 bu/acre.
Shallow soils (less than 24 inches) may be more prone to Zn deficiency. A with-the-seed or below-the-seed application of 5 lb Zn/acre should last for several years. With-the-seed applications may decrease the severity of Fusarium crown rot by approximately 10%. Foliar application rates are much lower than rates applied to soil, so repeat applications in following years may be necessary. First-time applications of zinc should be limited to small acreages.
For more information
Brown, B.D., M.J. Westcott, N.W. Christensen, W.L. Pan and J.C. Stark. 2005. Nitrogen management for hard wheat protein enhancement, PNW 578.
Christensen, N.W., R.G. Taylor, T.L. Jackson, and B.L. Mitchell. Chloride Effects on Water Potentials and Yield of Winter Wheat Infected with Take-all Root Rot. Agron. J. 73:1053–1058.
Cook, R.J. and R.J. Veseth. 1991. Wheat Health Management. The American Phytopathological Society, St. Paul, MN, APS Press.
*Douglas, C.L., D.J. Wysocki, J.F. Zuzel, R.W. Rickman, and B.L. Klepper. 1990. Agronomic zones for the dryland Pacific Northwest, PNW 354.
Cappellazzi, S., C. Sullivan, G.B. Jones and L. Brewer. 2024 Get actionable results from a soil, plant or environmental testing lab, EM 8677.
Horneck, D.A., D.M. Sullivan, J. Owen and J.M. Hart. 2019. Soil test interpretation guide, EC 1478.
Nibler, F.J. Fertilizer requirements of wheat grown under conservation tillage. M.S. thesis, Oregon State University, 1986.
Petrie, S.E., P.M. Hayes, N.W. Blake, A.E. Corey, K.E. Rhinhart, and K.G. Campbell. 2004. Chloride Fertilization Increased Winter Wheat and Barley Yield in Northeastern Oregon. In: Columbia Basin Agricultural Research Center Annual Report, 2004. Oregon State University.
Rasmussen P.E. and P.O. Kresge. 1986. Plant Response to Sulfur in the Western United States. In: Sulfur in Agriculture. M.A. Tabatabai (ed.). Agronomy Monograph (27). ASA-CSSA-SSSA. Madison, WI.
Stoskopf, N.C. 1985. Cereal Grain Crops. Reston, VA, Reston Publishing Company Inc.
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