June 22, 2008
The question of how much nitrogen is lost from fertilizer urea when it is applied to the soil surface comes up between growers and their nutrient dealers each year.
With the rising cost of fertilizers for agriculture, a Montana Agricultural Experiment Station investigation in the north state could shed light on how to reduce such losses.
Volatilization occurs after the fertilizer dissolves and urea changes to form ammonium carbonate. The process decreases soils acidity, causing ammonium to convert to gas, which escapes into the atmosphere.
Since surface urea applications are common in Montana, the study could have important new information for many growers. In winter wheat production systems, applications are often applied post-seeding during the fall, winter or in early spring. This year, the station began to study to quantify these losses for dryland winter what producers in Montana.
Ammonia losses are estimated using a micrometeorological technique known as the "integrated horizontal flux" method, which uses a mast with shuttles or passive samplers at five heights above the soil surface.
This spring, the system was used for the first time in Montana at Less and Terry Kaercher's farm near Havre, Mont.
Ammonia loss results show that 8.4% of the applied urea nitrogen volatized during the eight-week gas sampling campaign. No significant fertilizer induced ammonia losses occurred during the first two weeks following fertilization, however, because it never rained and there was insufficient humidity to dissolve the fertilizer.
Results from this first look at ammonia volatilization were labeled "somewhat surprising" by researchers in that it showed "significant" losses for many weeks following fertilization. Extreme drought, however, may have elevated these numbers.
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