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No. 14
Crop Fertilization and Air Quality
Fertilization, including both organic and inorganic sources, accounts for nearly 40% of crop yield in North America. In some countries, up to 75% of total production is the result of fertilization. Obviously, proper nutrient use is essential if farmers are to continue to grow sufficient amounts of food to meet the needs of a growing world population. Without adequate fertilization, billions of people could face starvation.
At the same time, the use of nitrogen (N) fertilizers, particularly animal manure and other organic sources, can also impact environmental quality by returning certain global warming gases back to the atmosphere. The three gases of primary concern are nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2). In addition, significant amounts of gaseous ammonia (NH3) can be released into the air as a result of crop fertilization. With careful management, NH3 losses are minimal.
All forms of N fertilizers—inorganic and organic—have the potential to release N2O to the atmosphere. However, direct loss of N2O from fertilizer is usually less than 1%. Other factors, such as cropping systems, soil management, and unpredictable rainfall have a much greater influence on N2O losses than do the various inorganic nitrogen fertilizer sources.
Liquid manure can greatly increase the rates of N2O loss. In one southeastern U.S. study, high rates of liquid manure produced denitrification rates 10 to 100 times higher than those resulting from the application of inorganic N fertilizers. Denitrification is a key step in the production of N2O in the soil and, thus, its loss to the atmosphere.
Methane gas released to the atmosphere because of agricultural production comes predominately from ruminant animals, livestock manure, wetlands, and rice production. Very little is associated with crop fertilization.
 
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