The time for the first application of nitrogen (N) to winter wheat is approaching. Split N application is typically the best management approach to maximizing yield and minimizing N loss. Nitrogen application should occur around Feekes 2-3 (typically mid-February to early March) and again at Feekes 5-6 (typically mid to late March) with the N split roughly 1/3 in the first, and 2/3 in the second, applications. Wheat stands that are thin or exhibit too-little tillering should receive higher rates of N in the first application to encourage tillering. Although N rate is an important consideration in setting up the crop for success, the purpose of this article is to discuss environmental conditions and potential outcomes from the first application, particularly this year.
Late winter can be difficult finding soil conditions suitable to support fertilizer applicators used to apply N. Often the soil is wet, resulting in ruts or compaction from equipment traffic. Some producers will take advantage of frozen ground to support N application to avoid creating ruts or causing compaction. The remainder of this article will discuss this practice and potential impacts that might arise from frozen ground nutrient application.
Nutrient management guidance from NRCS (590 Conservation Practice Standard https://www.nrcs.usda.gov/wps/portal/nrcs/main/ky/technical/ecoscience/nutrient/), advises against nutrient applications to frozen or saturated ground. The reason for this is the potential for nutrient runoff loss when a nutrient application is followed by rainfall before the ground thaws. When the soil is frozen, precipitation is not able to infiltrate and surface water runoff occurs. This surface runoff can contain soluble, recently applied nutrients and move these to adjoining properties and surface water, leading to degraded water quality.
Some producers might make N applications in the morning to frozen soil that then thaws in the afternoon. While by definition this is still a frozen ground nutrient application, the potential for nutrient loss is minimal compared to current soil conditions where the ground is frozen solid and will remain so for many days.
In 2014, a considerable amount of ground in western Kentucky was frozen to a depth of 6 to 9 inches. A study investigated the potential for N loss when several N rates were applied to frozen soil and were followed by significant rainfall. Approximately 3 inches of rain, followed by 1.6 inches of snow, fell while the ground was still frozen. The N applications made to frozen soil resulted in 40 to 70% less nitrate in the surface 12 inches of soil and 9% lower wheat yields compared to N applications made after the soil thawed. More details regarding this study can be found at the following the link: wheatscience.ca.uky.edu
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