AMMONIA LOSS FROM APPLICATIONS OF UREA-AMMONIUM NITRATE SOLUTION TO STRAW RESIDUE.

The increased use of urea and urea-based N fertilizers along with an increase in crops under no- or reduced-tillage practices may require changes in fertilizer management practices. Surface application of urea-based fertilizer risks the loss of some N by volatilization of NH//3. Our objectives were to assess the loss of NH//3 and to simultaneously observe the associated N transformation and movements in the field following broadcast applicaton of urea-ammonium nitrate solution at a rate of 200 kg N ha** minus **1 to soil with wheat (Triticum aestivum L. ) straw residue cover. Also, we wanted to characterize the factors associated with the residue that might affect loss. A micrometeorological mass-balance method was used to measure NH//3 loss during two sequential field studies with different amounts of precipitation and irrigation. Volatilization losses showed diurnal patterns coinciding with fluctuations in residue temperature, residue water content, and wind speed.