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Nitrogen Management

Transformation of Fall-Banded Urea

Application Date, Landscape Position, and Fertilizer Additive Effects

^a Dep. of Soil Science, Univ. of Manitoba, 362 Ellis Bldg, Winnipeg, MB, Canada, R3T 2N2
^b Agriculture and Agri-Food Canada, Brandon, MB, Canada R7A 5Y3
^c Western Co-operative Fertilizers Limited, Calgary, AB, Canada

^* Corresponding author (Don_Flaten{at}umanitoba.ca)

Received for publication November 8, 2005. A 2-yr study was initiated in the fall of 2000 to generate fundamental information on the effects of application date, landscape position, and a combined urease and nitrification inhibitor (NBPT [N-(n-butyl) thiophosphoric triamide] and DCD [dicyandiamide], respectively) on the rate of transformation of fall-banded urea fertilizer into NH₄⁺ and eventually NO₃^– under conditions typical for Manitoba, Canada. Landscape position did not have a large effect on the conversion of banded urea to NO₃^– under the moisture conditions present during the autumn period at the sites. Delaying application of fall-banded urea fertilizer into the late fall and the presence of NBPT and DCD slowed nitrification and increased the recovery of fertilizer N as NH₄⁺ (%RFN as NH₄⁺) in the soil before it froze. Date of application, the soil temperature on the date of application, and the accumulation of SHU (soil heat units) and NHU (nitrification heat units) were all linearly related to the %RFN as NH₄⁺. Accumulated SHU and NHU were most strongly correlated with the %RFN as NH₄⁺ at the end of the fall, with and without inhibitors. The interactions between time, temperature, and nitrification demonstrate that producers in the Northern Great Plains region must consider the overall length of time that fall-applied N fertilizer will be exposed to the soil before the soil freezes, even after the soil temperature has reached a given level and even if the fertilizer is banded.

Abbreviations: DCD, dicyandiamide • NBPT, N-(n-butyl) thiophosphoric triamide • NHU, nitrification heat units • RFN, recovery of fertilizer nitrogen • SHU, soil heat units

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				K. H. D. Tiessen, D. N. Flaten, P. R. Bullock, C. A. Grant, R. E. Karamanos, D. L. Burton, and M. H. Entz Interactive Effects of Landscape Position and Time of Application on the Response of Spring Wheat to Fall-Banded Urea Agron. J., May 7, 2008; 100(3): 557 - 563. [Abstract] [Full Text] [PDF]