Urea, when used properly, can be an effective way to fertilize established crops.
For years, ammonium nitrate, or 34-0-0, was the preferred fertilizer for use on pastures, hay fields and winter cereals. It was considered the most efficient broadcast nitrogen fertilizer for these situations.
When granular 34-0-0 was discontinued in Western Canada, urea, or 46-0-0, became the only practical alternative fertilizer.
Many producers are concerned about using urea because it is prone to losses and could ultimately increase their fertilization costs. However, these worries may not be justified.
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“Nitrogen in broadcast urea can volatilize or gas off and be lost to the atmosphere,” said Doon Pauly, crop specialist with Alberta Agriculture in Stettler.
“The severity of this loss depends on soil factors such as texture, acidity, organic matter content and environmental factors, namely soil temperature, wind, drying conditions and precipitation soon after fertilization. Many of these aspects are beyond a producer’s control, but the timing of fertilization can be managed.”
Applying urea to cold but not frozen soils at temperatures below 10 C is the primary way to minimize losses.
Research from Manitoba indicates that volatile losses from urea applied to cold soils are minimal during the first five days after application, but 25 to 35 percent nitrogen losses can occur in the first five days on warm soils with temperatures greater than 15 C.
Producers concerned about the efficacy of broadcast urea will need to ensure that the urea is applied to cold soils.
“Precipitation, either as rain or wet snow, is always needed to move surface applied urea into soil so it does not gas off,” Pauly said.
“On warm soils, it is essential that this precipitation occur within a day or two of application to minimize losses. On cold soils, the critical window for rain or snow is a little wider, perhaps as long as five to seven days after application.”
To maximize efficiency and minimize losses, urea must be applied to cold soils when there is a good chance of precipitation.
