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Issue No. 5, Article 12/April 23, 2004

Nitrogen Loss Associated with Surface Application of Urea and Urea-Containing Fertilizers

A portion of the nitrogen in urea-containing fertilizers, either granular urea or urea-ammonium nitrate solutions (28 or 32% N), which were surface applied and not incorporated, was likely lost during the extended dry, abnormally warm period of the last 2 weeks. Factors that influence the rate of loss include amount of residue cover, time between fertilizer application and rain, rate of application, and form of N applied. If the field was clean-tilled, the amount of loss, irrespective of these factors, will be very low--less than 5%. However, if there was substantial residue cover (greater than 20% residue), the losses could range from 5% to 40% of the urea N applied (Table 4). The amount of N loss from surface-applied urea is related to the rate of N application. Losses are very minimal at N rates of less than 100 pounds per acre.

If the urease inhibitor AgrotaiN was included with the fertilizer, loss of surface-applied urea would be negligible. Laboratory research conducted at North Dakota State University suggested that ammonium thio-sulfate (ATS) would markedly reduce ammonia volatility from urea. Unfortunately, research conducted by several universities has not confirmed that ATS will reduce N loss under field conditions from surface application of urea-containing materials.--Robert G. Hoeft

Robert Hoeft

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