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Winter Urea Fertilizer Application
Wet fields in some areas of North Dakota this fall prevented nitrogen fertilizer application. It may be tempting to apply urea fertilizer to frozen soils. There are two reasons why this is not a good idea. First, when urea is surface applied to soils which are deeply frozen and the urea cannot move down with the melt water, fertilizer will move sideways down slope instead. Secondly, urea is not very tightly held by soil until it hydrolyzes into free ammonia. This hydrolysis is not very temperature dependent. At temperatures above but near freezing, most of the urea can turn into free ammonia within two weeks. When it turns into free ammonia, it also raises the pH levels surrounding it. If the free ammonia is close to the soil surface, some losses are likely, particularly in soils with pH greater than 7.0. Therefore, winter urea application is recommended only when soils are thawed deeply enough to allow meltwater or rainfall to move the fertilizer into the soil to an average depth of about 1-2 inches.
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