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.


15 Feb 2010

2009 Annual Interpretive Summary

Ammonia (NH3) losses from urea have ranged from 3 to 40% of the application rate (19.4% average) over eight gas sampling campaigns conducted to date in 2008 and 2009. In this semi-arid region, NH3 losses are sometimes delayed by 2 weeks or more until sufficient precipitation falls to dissolve urea granules. Significant NH3 losses may then occur over a three to six week period. Applying urea to frozen soils does not guarantee losses will be minimized. Surprisingly, some of the greatest NH3 losses (e.g., 32, 36, and 40% of the application rate) occurred at three sites where urea was applied to moist surface soils near 0°C. Environmental conditions that result in prolonged damp conditions near the soil surface appear to promote volatilization losses. Ammonia fluxes as large as 22 kg N/ha/week have occurred under these conditions. Conversely, NH3 losses from surface-applied urea are generally smaller (<16% of the application rate) if granules are applied to dry soils. Coating urea with an urease inhibitor like N-(n-butyl) thiophosphoric triamide (NBPT) at 4.2 ml/kg provides 2 weeks of protection against volatilization losses following fertilizer dissolution, and has reduced NH3 losses by 62% over untreated urea.

Results from this study indicate that significant NH3 volatilization losses can occur from cold soils when urea is surface-applied. This study will be continued for one more year. MT-17