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.


16 Feb 2013

2012 Annual Interpretive Summary

In 2012, trials were conducted on a farm near Coffee Creek, Montana. The field site was under no-till management and was seeded to winter wheat. A mass-balance micrometeorological experiment was established to quantify ammonia (NH3) losses from urea and urea treated with NBPT [N-(n-Butyl)-thiophosphoric triamide]. Three application timings (fall, winter and spring) at 100 kg N/ha, with and without NBPT (1 g/kg), were made to circular plots (20 m radius) at this site. A closely located, replicated small-plot fertilizer experiment was established to measure crop yields. This study consisted of three urea surface-application times, two NBPT treatments (-, +), two N rates (50 and 100 kg N/ha), and a non-fertilized (0 N) control. The urea application timings in the small-plot study were paired with the applications in the micrometeorological studies such that fall, winter and spring applications occurred on the same dates. In addition, 15N-enriched fertilizer micro-plots were established inside of the small-plot study to determine the amount of applied fertilizer N that is absorbed by wheat and translocated to the crop grain and residue.

Ammonia losses were very modest for the spring campaign because a 24 mm precipitation event occurred within a few days following fertilization. The NH3 losses were 1.2% for regular urea compared to no loss for urea treated with the urease inhibitor NBPT. Large precipitation events will often incorporate urea into the soil where it is protected from volatility losses to the atmosphere. Cumulative NH3 losses for the fall and winter applications were 13.4 and 5.6% for regular urea compared to and 13 and 3% for urea treated with NBPT, respectively. Overall, grain yield and protein were responsive to N fertilizer as anticipated due to the low indigenous soil N levels (19.3 lb N/A in the upper 24 in. of soil) at this field site. Grain yield averaged 31.1, 46.1 and 52.5 bu/A for the 0, 50 and 100 kg N/ha rates, respectively. Average fertilizer N recovery in grain for the N application times of regular urea compared to urea treated with NBPT were respectively, 27 and 38% for fall, 27 and 37% for winter, and 45 and 48% for spring. It is planned to continue this study for two more years on adjacent fields at this location. MT-17