Soil and Nutrient Management for Winter Wheat

KEY POINTS

• Nitrogen is often the most limiting nutrient for winter wheat production and can cause lower yields, lower protein levels in the grain and leaf yellowing, which can lower plant biomass.
• Winter wheat has a low, but needed, phosphorus demand. It is recommended to incorporate phosphate and potash fertilizer before seeding.
• Wheat grows best in well-drained, slightly acidic to neutral pH soils like loam or clay loam. Wheat can also grow in sandy soils if effectively managed and irrigated.

Introduction

Winter wheat is primarily produced for grain across the United States and southern Canada. Production has expanded in recent years as winter wheat is used for forage for grazing, silage, hay, and as a cover crop. Winter wheat varieties are sown in the fall and usually become established (fall tillering growth stage) before going into dormancy when freezing weather arrives. Freezing events that occur after germination cause the winter wheat to go through a vernalization process that is needed to promote flowering in the spring.

Wheat production in the U.S. is ranked third behind corn and soybeans in planted acreage, production, and gross farm receipts. Wheat is divided into five types:

1. Hard red winter wheat (HRW)
2. Hard red spring (HRS)
3. Soft red winter (SRW)
4. Hard and soft white (both winter and spring)
5. Durum¹

Around 40% of total wheat production produced in the U.S. is hard red winter wheat and most of these production acres are in the Great Plains states of Kansas, Colorado, Nebraska, Oklahoma, Texas, Montana, North and South Dakota and Wyoming. There is also limited production in the Pacific Northwest (PNW) and California, which makes it the most widely grown wheat class in the United States. Soft red winter wheat in the U.S. is typically produced in areas east of the hard red winter wheat growing areas, all the way to the east coast. Combining soft red winter wheat, soft and hard white winter wheat, and hard red winter wheat into a winter wheat class represents an average of 70% of total U.S. wheat production.¹

Soil Fertility

Soil Testing

A soil testing program provides valuable information for the fertility requirements required for a high yielding winter wheat crop. Accurate soil testing requires representative samples, accurate laboratory testing, and meaningful interpretations.

Representative Samples

There are important soil sampling guidelines and procedures to follow to help ensure soil testing accuracy to get the results needed to make effective fertility management decisions. A good soil sampling guide can be found at Soil Testing 101. When soil testing for winter wheat, the sample should be divided into two separate samples: a surface sample from 0 to 12 inches deep and a deep soil sample from 12 to 24 inches deep. A deep soil sample can help provide a more complete picture of the availability of nitrogen (N) that a winter wheat crop may use which can reduce the total amount of N fertilizer required. Not taking residual N into consideration can lead to overfertilization which increases production expenses and cause lodging problems prior to harvest, reducing yield potential.²

Accurate Lab Analysis

Using a local soil testing lab can help improve accuracy as a local lab understands the soil characteristics native to the area and can use testing procedures to better predict the availability of nutrients important for plant growth.

Meaningful Interpretations

It is important to use the fertility recommendations from the soil testing lab used, for the crop indicated and at the desired yield goal. Nitrogen (N) is often the most limiting nutrient and should be the first nutrient to address. The N requirements for a winter wheat crop roughly starts with 1.75 pounds of N for each bushel of wheat.³ A 60-bushel wheat crop requires 105 total pounds of N per acre. The soil test will determine the amount of residual N that is in the soil sample and subtract it from the total required N. Any N credits from a previous crop or manure applications should be deducted from the total N required to reach the yield goal. Organic matter (OM) levels are often included in the soil test and can be used to determine the residual N available during the growing season as an N credit is associated with the OM level. Over time OM releases N through the mineralization process. Approximately 30 pounds of N can be released per acre per year for each 1.0 percent of OM in the surface soil layer.⁴ Fertilizer recommendations should consider N credits from previous crops, manure applications, and OM content when considering the total N required to reach the yield goal. Results for nutrients other than N will often be listed as a very low, low, medium, high, or very high levels. Soil testing labs use years of fertility studies to correlate the lab results to expected crop response and to various fertilizer application rates. Recommendations for fertilizer application amounts for each nutrient are provided for the crop to be produced and at the yield goal desired.

Nitrogen Application Programs

Winter wheat producers often use a total pre-plant N fertility program. Depending on the tillage used, soil type and the amount of precipitation that is received prior to the spring rapid growth stage, this can be a viable fertility program. Before implementing a total pre-plant N program, producers should consider the potential for N losses that can occur under certain growing conditions.

Most wheat crops require a limited amount of N in the fall to stimulate growth and tillering. If a soil test is not available to determine the residual N in the surface soil profile, then a minimum of 30 pounds N per acre applied pre-plant or at planting should be enough to supply those early plant needs. The applied N should not be in direct contact with the seed as it can cause seedling fertilizer burn and reduce the plant population.

A top-dress N program for winter wheat in the spring is especially important for crops grown on a light or sandy soil type or on poorly drained or claypan soils. Sandy soils with excessive spring moisture can push N below the root zone of the growing wheat plants and be lost to that crop. In heavy clay soils, a second type of N loss mightoccur, denitrification. If there is excessive spring moisture, the early applied N can be lost by denitrification, as the N is converted to a gas in water saturated soils and lost into the atmosphere. By top-dressing N, it allows the producer to match the N fertility program to the yield potential of the crop as it breaks winter dormancy and either increase or decrease nitrogen rates based on crop and environmental conditions. A top-dress application, when applied after the crop greens up but before it starts to joint (Feekes 4-5), places this important nutrient in the soil just prior to the crop use, which reduces the potential for nutrient loss. N applied after the crop starts to joint (Feekes 6), often has limited yield response unless the crop is severely deficient in N.

When applying N to a growing wheat crop, there is a potential for leaf burn to be observed. There are several ways to help reduce leaf burn potential, including:

1. Applying liquid N with steamer nozzle to keep the majority of N off the green leaf tissue.
2. Applying granular N fertilizer with a dry fertilizer applicator.
3. Applying urea ammonium nitrate (UAN) through a center pivot irrigation system if available.
4. Applying a diluted 1:1 mixture of liquid N fertilizer and water to reduce the concentration.
5. Applying N when the weather is cool, non-humid, and calm and avoid top-dressing N on hot, windy days.⁵

In a no-till wheat production system, if liquid N is applied to the soil surface, it can be tied up, or immobilized, on the high amounts of crop residue. This N that is tied up will not be immediately available to the growing crop so a top-dress application of an additional 20 to 30 pounds of N per acre, prior to the rapid plant growth in the spring is often beneficial. This additional N can help the crop green up and find the N needed for spring growth. When utilizing equipment that injects the N fertilizer below the residue mat, as a pre-plant or side-dress N application, this type of equipment places the N in the soil and will reduce this residue N tie-up problem. If this type of equipment is used as a side-dress application, be careful to set the equipment just deep enough to cut through the residue to help limit soil movement and stand damage. A nitrogen application program developed at the University of Nebraska is available for winter wheat, at https://cropwatch.unl.edu/nitrogen-management-winter-wheat.

Additional Fertility Recommendations

Using soil test results and fertilizer recommendations from the lab, any additional fertilizer should be applied prior to wheat planting or added to an early N top-dress application, depending on the nutrient being applied.

Phosphorus (P) is essential for root development, tillering and resistance to winterkill. Since it is a very immobile nutrient in the soil it is important to place the P fertilizer in the soil at a depth where wheat roots can reach it. If soil test levels are extremely low, a band application near the seed placement may allow for a one-third reduced application rate, but this reduced application rate will not increase soil test levels over time.

Potassium (K) should also be applied before planting if soil test levels are low. Many soils have enough K levels in the soil to support a high yielding winter wheat crop. The exception to this general observation is when the crop is grown on sandy soils or fields that have a history of multiple years of continuous soybean production.⁴

Sulfur (S) is the third major crop nutrient that may need to be included in a nutrient management plan for winter wheat. This is one nutrient that a soil test may not be a good predictor for a crop response to a deficiency. Sulfur is very mobile in the soil, and if the crop is being grown on a sandy or sandy loam soil with less than 3% organic matter, this along with above normal precipitation, can reveal a S deficiency. Sulfur deficiencies often show up during early spring growth as stunted plants, yellow growth, and thin spindly stems, which can result in delayed maturity. A crop exhibiting these symptoms as it is breaking dormancy and greening up, can benefit from a base application of ten pounds of S in an early top-dress fertilizer application. Ammonium thiosulfate (ATS) fertilizer is a liquid formulation of S that is highly plant-available but can cause leaf burn like some liquid N sources and must be managed to address these concerns.

Copper (Cu) is a nutrient that has seen only sporadic yield response and only then on a low-organic matter, sandy soil. If Cu is applied as a copper sulfate application, a rate of five pounds of Cu per acre pre-plant can help correct this deficiency. This amount of Cu fertilizer, when applied, can last for multiple years.

When a chloride (Cl) deficiency is corrected for a wheat crop, a yield increase of two to five bushels per acre has been observed, but only about half the time. This yield increase is often attributed to improved plant resistance to certain leaf and root diseases, which can show up as an increase in kernel size.

Other crop nutrients such as zinc, iron, manganese, or boron have not commonly shown a yield response when added to a wheat fertility program. It is thought that most western soils supply enough of these nutrients and supplemental application is not necessary.

Soil Management

Wheat can be grown successfully on most soil types. A fertile, deep, loam soil with good internal drainage is often considered the best soil to grow a wheat crop. However, many other soil types that include various amounts of sand, silt, or clay, and different fertility and management requirements, can successfully grow a winter wheat crop, if managed correctly. There is one soil type, classified as a peat soil, which can have elevated levels of iron, sodium, and manganese, has been identified as unfavorable for wheat production.⁶

Soil pH Requirements for Winter Wheat Production

The optimum soil pH for wheat production is between 5.5 and 7.5.⁶ Soil test results can establish the pH of the soil sampled and determine the amount of lime required to correct a low pH soil or acidic soil condition. Growing wheat in acidic soils with a pH of less than 5.5, can lead to increased solubility of aluminum, manganese, and iron which can be toxic to the plant and reduce plant growth and yield potential. A low pH soil can be adjusted to recommended values by liming the soil in the fall prior to planting with a limestone (calcium carbonate) or magnesium carbonate application. The amount of lime required depends on the initial soil pH, soil type and the buffering capacity of the soil along with the quality of the agricultural lime source (the purity and how finely the lime has been ground). Winter wheat produced on alkaline soils, with a pH of 7.5 or higher, can cause a reduced availability of certain micronutrients such as iron, zinc, and manganese. Also, the availability of phosphorus can vary as the pH of the soil increases.

Salinity Concerns

Saline soils is a problem that can show up when the crop is irrigated with a water source with a high salt load and in soils with poor internal drainage. Higher levels of soil salinity lead to decreased moisture absorption from the soil into the plant, impeding plant growth. Soil salinity is measured by the electrical conductivity (EC) of the soil solution water in the soil. Wheat has above average soil salinity tolerance. This means that a soil with up to an EC of 6.0 will not have a yield effect on wheat crop, while that same 6.0 soil EC will have a 50% relative yield decrease for a corn crop. When growing a wheat crop in a soil with a salinity of 13.0, an expected relative yield decreases of 50% can be expected.⁷

Sources:

¹ 2024. Wheat sector at a glance. USDA Economic Research Service. U.S. Department of Agriculture. https://www.ers.usda.gov/topics/crops/wheat/wheat-sector-at-a-glance/

² Wheat fertility. Kansas State University. Kansas State Research and Extension Sunflower District. https://www.sunflower.k-state.edu/agronomy/wheat/wheat_fertility.html

³ 2023. Soil fertility and plant nutrition. Servi-Tech. Crop Files. Agronomic Commodity Crops. https://cropfile.servitech.com/crop-files/1-00-soil-fertility-plant-nutrition.

⁴ Davis, J.G., and Westfall, D.G. 2014. Fertilizing winter wheat. Colorado State University. Corado State University Extension. https://extension.colostate.edu/topic-areas/agriculture/fertilizing-winter-wheat-0-544/.

⁵ De Olivera Silva, A. 2021. Time to top dress wheat. Oklahoma State University. https://osuwheat.com/2021/01/15/time-to-topdress-wheat-2/.

⁶ Cherlink, V. 2023. How to grow wheat efficiently on a large farm. ESO Data Analytics. Crop Cultivation. https://eos.com/blog/growing-wheat/.

⁷Cardon, G.E., Davis, J.G., Bauder, T.A., and Waskom, R.M. 2014. Managing saline soils. Colorado State University. Extension. https://extension.colostate.edu/topic-areas/agriculture/managing-saline-soils-0-503/.

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