Winter Fertilization Facts

Fall and winter broadcast application of urea (46-0-0) continues to take place on various winter wheat farms across Chouteau County. The major concern of broadcasting urea is nitrogen loss through ammonia volatilization. Volatilization results when there is a conversion from dissolved ammonia to ammonia gas. From 2008-2012, Rick Engel and Clain Jones (MSU Soil Scientists) have studied NH3 losses from surface-applied urea. Below are a few conclusions of their research.

• Engle’s research (4 years and 20 studies) documented a range of 1-44% volatilization of broadcasted urea. The average volatilization of urea was 20%.

• Volatilization can be minimized by applying urea under dry soil conditions. Cumulative NH3 losses were less than 20% when applied to dry soils. If ½ inch of rain fell on the dry soil after application, NH3 losses were less than 10% of applied Nitrogen.

• Ideally, urea should be incorporated or subsurface applied to minimize losses.

• Urea applications to moist, high water content soil resulted in large NH3 losses as high as 44% of applied Nitrogen. Volatilization increases when the soil is moist or frozen and no major precipitation takes place.

• Cold soil conditions do not provide protection against large NH3 losses from surface-applied urea.

• Agrotain® reduced NH3 volatilization losses from urea by approximately 2/3 over untreated urea.

• Volatilization protection from Agrotain® is approximately two weeks on acidic soils, but longer on calcareous soils.

Information for this article came from Montana State University Extension and Agricultural Experiment Station Fertilizer Fact sheets 59 and 60, which are available upon request from the Chouteau County Extension office.