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.
IPNI-2008-USA-MT17
22 Feb 2011
2010 Annual Interpretive Summary
Ten field investigations [i.e., ammonia (NH3) gas sampling campaigns] have been completed as part of this project over the past 3 years. The magnitude of N losses due to ammonia volatilization are quite variable and very much dependent on the soil moisture conditions, rainfall, and climatic conditions that are experienced following application of the fertilizer granules. The best example of this is provided by the contrast in results from Campaigns #2 and #5. These investigations were carried out at the same field site, yet N losses from urea differed by more than 10 times (3.1% versus 39.9%) between the fall and spring applications, respectively. Surface soil moisture conditions at time of fertilization were dry and fertilizer granules remained undissolved and visible for 24 days during Campaign #2. Beginning on November 2, 0.98 in. of rain fell over a 67 hour period, which was sufficient to dissolve the fertilizer granules and transport the urea to a depth in the soil profile where it was protected from volatilization losses. In contrast, the spring fertilizer was applied to the soil surface with a trace of snow (Campaign #5). Although the surface temperatures were at 31 ºF (-0.6 ºC), the fertilizer granules began to dissolve almost immediately, but ammonia volatilization losses during this campaign were extremely large, because only light precipitation was received over the first month (e.g. 0.3 in.), and fertilizer N remained exposed near the surface and were subject to volatile ammonia losses when urea hydrolysis occurs from the action of soil and crop urease activity.
Enough research data is being gathered to categorize and determine what weather conditions allow ammonia volatilization conditions to exist, and planned research in 2011 will expand this information to allow formulations of recommendations to farmers on how to reduce the risk of ammonia volatilization. MT-17