Agricultural Nitrogen and Emissions to the Atmosphere

DAVID FOWLER, MARK A. SUTTON, UTTE SKIBA AND KEN J. HARGREAVES 

The interest in gaseous losses of nitrogen from soil is now extensive and includes the well established community of soil scientists concerned with losses of fertilizer-applied nitrogen by nitrification and denitrification. More recently, interest in ammonia losses from plants and soil has been stimulated by the very large emissions from intensive cattle production in the Netherlands and their 

Smith and J. R. M. Arah, Losses of Nitrogen by Denitrification and Emissions of Nitrogen Oxides from Soils, The Fertiliser Soeiety, 1990, Proeeedings No. 299. 

The early measurements therefore identified NHj volatilization, and were followed in the f920s by studies which demonstrated NHj emission by vegetation. The measurement of emission of NjO and NO from agricultural sites has been 

The agricultural emissions of NHj, NjO and NO must be considered in context the processes which lead to net loss from the soil and vegetation are natural and form a part of the land-atmosphere cycling of this vital nutrient. The current agricultural processes, however, create conditions in which the small natural background fluxes, in the range of a few ngNm s are dwarfed by losses from fertilized land. 

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Often, the rates of fertilization in intensively managed agriculture are intended to satiate the needs of crop plants for these chemicals, so their productivity will not be limited by nutrient availability. However, excessive rates of fertilization have important environmental costs. These include the contamination of ground water with nitrate eutrophication of surface waters caused by nutrient inputs (especially phosphate) acidification of soil because of the nitrification of ammonium to nitrate large emissions of nitrous oxide and other nitrogen gases to the atmosphere, with implications for acid rain and Earth s greenhouse effect and the need to use herbicides to control the weeds that flourish under artificially nutrient-rich conditions. 

During the past twenty five years acid rain, formally referred to as acid deposition, has been the focus of much political debate and scholarly research. Acid deposition occurs when important precursor pollutants, such as sulfur dioxide (SOj) and nitrogen oxides (NOx), chemically mix with water vapor and oxidants in the atmosphere and fall back to earth in wet or dry form. Wet deposition comes in the form of dew, fog, snow or rain, while dry deposition occurs as either gasses or dry particulates. Research has shown that acid deposition adversely affects freshwater lakes and streams, coastal habitats, agricultural production, forests, soils, human health and building materials. Fossil-fuel power plants, refineries, and paper and pulp mills are the major sources of SOj emissions, while automobiles and other vehicles are the primary emitters of NO. ... 

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