A Micrometeorological Study to Quantify Ammonia Volatilization Losses from Surface Applied Urea in the Semiarid Northern Great Plains

Montana winter wheat growers broadcast surface apply urea to their crops in late fall, or early spring to supply the crops with needed nitrogen. Urea is known to be susceptible to ammonia (NH3) volatilization losses, no studies have specifically targeted the measurement of these losses from cold soils ( 10°C). This study is being conducted to quantify NH3 emissions from surface applied urea to no till winter wheat; and to evaluate the efficacy of NBPT (N-(nbutyl) thiophosphoric triamide) to mitigate potential ammonia volatilization losses made during colder weather periods.


02 Feb 2009

2008 Annual Interpretive Summary

Top-dress or surface application of urea is a common practice for Montana’s winter wheat producers. However, urea applied to the soil surface is susceptible to volatilization losses as ammonia (NH3-N). The objective of this study is to quantify the extent of ammonia loss from top-dress urea applications, applied in the early fall, late fall, and early spring to winter wheat using a mass-balance micrometeorological approach referred to as the integrated horizontal flux (IHF) method. This method involves sophisticated calculations based on airflow at the site measured at three heights on a mast located in the center of the 100 m diameter treatment area. Two research sites were established near Havre, Montana, in the fall and early winter of 2008. Each site had three macro-field applications of urea-N fertilizer including a control with no urea applied, 100 kg N/ha of urea, and 100 kg N/ha using urea treated with Agrotain®.

Ammonia losses were greatly affected by the timing and amount of precipitation received at the respective sites. Weather at the site located west of Havre was initially very dry, with no rain occurring for three weeks following the N application on October 9. During this time, urea granules remained on the soil surface and never dissolved and no ammonia emissions were detected. After 38 mm of precipitation (snow and rain) between Nov 2 and 9, sufficient urea moved into the soil, but ammonia losses from this site have been small (about 3.1% of the applied N rate for the urea treatment). Results were quite different at the second field site located north of Havre. Urea and Agrotain®-treated urea were applied to moist ground on November 14. Urea granules dissolved within the first day and ammonia losses from untreated product over the next three weeks amounted to 29% of application rate. Losses from Agrotain®-treated urea were one-tenth as high so it appears that the addition of Agrotain® can significantly reduce urease activity and the associated volatile ammonia losses. MT-17