NITROGEN MOBILIZATION IN THE UNITED-STATES-OF-AMERICA AND THE PEOPLES-REPUBLIC-OF-CHINA

Through fossil-fuel combustion, commercial fertilizer production, and legume and rice cultivation, humans are mobilizing nitrogen (N) at sca les that exceed natural terrestrial rates. Globally, approximate to 14 0 Tg of reactive N are mobilized each year; activities in the People's Republic of China (China) and the United States account for approxima tely 30% of this reactive N. This paper compares N mobilization rates and nitrogen oxides (NOx) and ammonia (NH3) atmospheric emission rates for China and the United States over the last few decades and project s the rates to the year 2020. We have estimated that the United States and China currently mobilize about 20 and 25 Tg N yr(-1), respectivel y. In the United States, commercial-fertilizer use accounts for about 50% of the annual total; in China, it accounts for about 80%. N emissi ons to the United States atmosphere are dominated by NOx. China's N em issions are dominated by NH3 from fertilizer use and domestic animal w aste. If recent trends continue, we have projected that by 2020 N mobi lization in the United States will differ little from current levels a lthough N mobilization in China will increase significantly because of increased fertilizer use and fossil-fuel combustion.