Agricultural Nitrogen Budget in the Yangtze River Basin from 1990 to 2000
For the purpose of estimating the amount of nitrogen (N) added to the agroecosystem by human activities in the Yangtze River Basin, and analyzing temporal and spatial changes of N budget in the Yangtze River Basin from 1990 to 2000. Following the mass balance model, a complete N budget was established for the Yangtze River Basin. N input sources include inorganic fertilizer, atmospheric deposition, biological fixation, excrement as fertilizer, crop residue used as fertilizer and combustion of crop residue. N output sources include crop harvesting, denitrification of soil nitrate, and NH3 volatilization. The budget had been calculated as the difference between all inputs and outputs. The total N input was 13.03 Tg N and 17.71 Tg N in 1990 and 2000, respectively. The total N output was 6.83 Tg N in 1990 and 8.76 Tg N in 2000, respectively. The N budget was 6.20 Tg N in 1990 and 8.95 Tg N in 2000 in agricultural fields of the Yangtze River Basin.