Nitrogen losses are possible in Kentucky wheat fields where the operators applied nitrogen to frozen ground in January and February, contributing to a delay in the crop now.
“Though the soil was frozen enough to support sprayers, significant precipitation fell after the application was made. The nitrogen likely was not able to penetrate the soil and could have been lost to surface runoff,” said Edwin Ritchey, extension soil specialist with the University of Kentucky.
Ritchey, Carrie Knott, UK grain crops specialist and Lloyd Murdock, UK extension soil specialist, conducted a study at the UK Research and Education Center in Princeton to look at the potential nitrogen loss when applied to frozen ground.
They applied sodium nitrate to frozen wheat fields with Crider and Zanesville soil types on Jan. 31 at the UKREC. After the nitrogen was applied, several rain and snow events occurred, resulting in more than 4.5 inches of total precipitation. Specialists made sodium nitrate applications to adjacent thawed fields Feb. 24 for a comparison.
They collected soil samples from each field March 11. Nitrate losses were between 49 and 64 percent in soils that were frozen when the nitrogen application was made.
“Based on this limited data, it appears that a substantial amount of nitrogen was lost from the soil and was not utilized by the plants,” Ritchey said. “The use of sodium nitrate represents the maximum potential nitrogen loss. Other nitrogen forms could lose less”.
“As of March 20, much of the state’s wheat crop has only reached Feekes 2 or 3,” Knott said. “Compared to most years, this represents about a two to three week delay in growth.”
Common nitrogen sources used in wheat production are solid urea or a solution of urea and ammonium nitrate. “Ammonium forms of nitrogen could potentially be retained in the soil to a greater extent than the nitrate form, even with limited infiltration,” Ritchey said. “It is not known if or to what extent this occurred.”
UK specialists recommend producers making split applications put nitrogen on fields when the wheat reaches the growth stage between Feekes 2 and 3 and again when the plants reach between Feekes 5 and 6. Normally, the application time for both has already passed, but this year, the crop is behind.
Growers who made their first application during January or February should adjust their second application rates to compensate for the lost nitrogen.
“Although a substantial amount of the first nitrogen application might have been lost if applied to frozen ground, the yield potential has not been compromised,” Knott said. “There is still time to adjust nitrogen rates with the second application so that wheat yields are not limited.”