Raedan Sharry, Ph.D. Student, Precision Nutrient Management
Brian Arnall, Extension Specialist, Precision Nutrient Management

Note, this blog is focused on grain only winter wheat production.

Crop producers looking to increase profits often consider how to reduce costs without sacrificing yield and/or quality. This applies to essentially all production functions including nitrogen application. Winter wheat growers in the southern Great Plains have a wide number of options available to them when considering nitrogen source and application technique. At the time of writing (08/27/2021) fertilizer prices obtained from the Two Rivers Farmers Cooperative are as follows ($/unit): UAN (28-0-0) $0.62, NH₃ (82-0-0) $0.45, and Urea (46-0-0) $0.62. These price levels equate to approximately a 57% increase in urea cost, 65% increase in UAN28, and a 65% increase in NH

Application Timing

Winter wheat producers in the southern plains have historically applied nitrogen (N) fertilizer prior to planting, often utilizing anhydrous ammonia for application due to its generally lower price point per unit of N relative to other sources. However, research at Oklahoma State shows that if the total N application is delayed until approximately feekes 5 to feekes 7 stages (jointing) yields were increased 23% of the time while grain protein was increased 68% of the time. By delaying N application to later in the growing season N is more likely to be available when the crop requires by avoiding conditions conducive to losses. Further reading on delaying nitrogen application can be found here (https://osunpk.com/2020/09/10/value-of-in-season-application-for-grain-only-wheat-production/)

A study located a Perkins, OK observing yield and protein response provides an example of an expected response to delayed N. In this study 3 N fertilizer rates (180, 90 and 45/45 split) across 5 different timings (Pre, 30, 60, 90, and 120 days after planting) where investigated. Grain yield was maximized by the 180 lb. rate applied 60 days after planting, while protein was maximized at the 120 days after planting timing. This same trend continues across all N rate levels as the later N applications whether at 60 or 90 increased yield relative to the pre while the 120 days after planting application maximized protein level regardless of rate level. However, maturity of the 120 day application treatment was severely delayed. This experiment shows the ability to sustain yield while decreasing N rate if N application is pushed to later in the season to avoid conditions that lead to N losses as displayed by the 90 lbs. at 90 days after planting treatment compared to the 180 lb. pre-plant rate.

Application Cost

Application costs are directly related to choice of source utilized. For instance; anhydrous ammonia application is predicated on the use of a pulled implement such as a low disturbance applicator for in-season application or a tillage implement for pre-season application. This is compared to other sources such as urea or ammonium nitrate which may be broadcast, or UAN that can be applied using a sprayer. The relationship between source and cost of application is inherently related to the application efficiency of the equipment used. Table 2 below provides a rough idea of cost associated with different application methods. (Information Retrieved from Iowa State). Fuel cost assumed at $2.60/gal. Labor cost assumed to be $15.00/hr.

In many operations across the southern plains efficiency has become a key factor in decisions such as input selection and equipment purchases. This has come in response to the need to cover more acres with less labor. With that in mind and looking back to table 2 it is easy to see that a self-propelled sprayer is likely able to cover more acres than other equipment options. This most likely should be considered when considering options for N management in the wheat crop.

Summary

With wheat sowing quickly approaching for many and field preparation nearing completion it is important to consider your nitrogen management options. Delayed N application allows for flexibility in management plan and depending on source utilized may increase application efficiency over pre-plant applications requiring a tillage implement. As fertilizer prices continue to remain high it is also important to consider the likely increase in N use efficiency due to applying N closer to when N requirement is peaking. Controlling cost while continuing to maximize output is imperative to sustainable profitability in crop production.

Any Question or Comments please feel free to reach out me.
Brian Arnall b.arnall@okstate.edu