Nitrogen Fertilizer Recommendations for Winter Wheat

Our moist climate certainly increases the challenges associated with successful nitrogen fertilization of wheat. Therefore, using best management practices, such as split application of nitrogen fertilizer, are likely more important for wheat than any other crop, including corn. This is because wheat is grown during the wettest months of the year in our rainy, warm climate, which is normally very conducive to nitrogen loss. Therefore, most nitrogen fertilizer must be applied in the spring to moderate losses. As a result, nitrogen application timing can be very important, particularly for the first spring application. Optimal nitrogen timing can vary substantially because seasonal weather, planting date and variety all affect wheat development. Therefore, you can make better fertility decisions by closely monitoring wheat health and development, and evaluating the weather forecast, rather than relying on specific calendar dates and rate guidelines.

Although this publication focuses on nitrogen, don’t overlook other nutrients, as productivity will be reduced by whatever factor is most limiting. For instance, field areas where growth has lagged throughout the fall and winter could have other fertility issues, such as low soil pH, low phosphorus, etc…, which need to be addressed.

Split-application methodology for nitrogen fertilization of wheat is strongly recommended in our region.  This strategy satisfies crop demand, while moderating potential nitrogen loss caused by denitrification in saturated soils common during the spring. This may be achieved through two or more split fertilizer applications with at least 2/3 of the total spring nitrogen applied after stem elongation begins. Only a small amount of nitrogen is necessary in the first spring topdress application (20-30 lbs. N/a.), because wheat nitrogen needs are quite modest, until stem elongation and rapid growth begins. This initial nitrogen topdress should be applied when prostrate, tillering stage wheat (Feekes growth stage 3 or 4) breaks winter dormancy and slowly resumes growth.  Neglecting wheat nutritional needs during this time may considerably limit the number of viable tillers that will produce heads and thus, are essential to high wheat productivity. If a field has a thin stand, poor tillering due to late planting, or signs of nitrogen deficiency, proper timing of this initial nitrogen application becomes even more critical. This supplemental fertility is needed to support wheat growth while it can compensate for these shortcomings by developing tillers. After stem elongation begins, primary nitrogen applications may proceed, as nutrient demand rapidly rises with increasing biomass production. A second nitrogen application should occur when plants become strongly erect and stem elongation begins, and again prior to boot stage, if you choose to make a third application.

Urea is the most commonly used nitrogen source on wheat because it is generally the most economical nitrogen source, it can be applied by air, and its volatility issues are relatively low during the early spring, when temperatures are cool and rainfall is frequent. Liquid nitrogen solution (UAN) can potentially burn leaf tissue, especially if high rates are broadcast on erect wheat, so granular nitrogen sources are generally preferred, particularly for single, or the later split applications.

Sulfur deficiencies continue to increase in prevalence, so it is becoming more prudent to address sulfur needs while applying nitrogen, particularly when wheat is grown on sandy or low organic matter soils. Ammonium sulfate or other sulfate forms of sulfur fertilizer should generally be applied in an early spring timing, because deficiencies typically occur during early vegetative stages (late February through March).  Sulfate forms of sulfur fertilizer are strongly recommended to address seasonal crop needs and deficiency cases, because they are immediately available for crop uptake, while elemental sulfur is not.

Our wet southern climate normally influences nitrogen use efficiency considerably depending upon seasonal rainfall frequency and amount.  Therefore, we have generally found nitrogen rate response is best correlated to soil texture, which influences water relations and potential nitrogen loss.  On the other hand, nitrogen rate guidelines based upon crop yield goal are not very reliable for wheat production in the South.  We normally suggest from 90 to 130 lbs. N/acre on light-textured soils and 120 to 150 lbs. N/acre on heavy clay soils. However, monitoring crop response to nutrition, culture and environmental conditions offers growers considerable opportunity to fine tune your fertility program.