| In order to establish the N cycling and balance model of "agriculture-livestock-nutrition-environment" system, the N flow in agriculture, livestock, human nutrition, waste water management, waste matter management and the whole system were studied respectively with several methods such as model analysis. literature materials analysis, statistic data packing up and so on. The N cycling and balance at national country scale in 2001 was calculated and the situation of the N flow in whole ecosystem was described. The results were as followed:1. The model of N cycling and balance has been established by confirming the parameters about the N cycling and balance. The model can be used to calculate the N cycling and balance in different years and analyze the N flowing and distribution in the whole ecosystem in China.2. In agriculture system, the N balance appeared evident surplus. In 2001, the surplus amount of N was 857.2 ×10~4 t. The major input of N was the N of fertilizer and manure and the percentage was 58.85% and 25.32% of the total input respectively. The percentage of other N inputs including the N of the N-fixation, dry and wet deposition and irrigation was 15% of the total input. The major output of N was the N in crop removal, account for 58% of the total output. The NH3 emission and denitrification of fertilizer is another important approach of N output in agricultural field. The percentage of the total output was 26%.3. The N of the feed is the major input and the amount N of feed is 1952.1 ×10~4 t in 2001. The N of the feed is the major input. In the output items, the N of animal excretion is the primary one which occupied 70% of the total output N in livestock system. The amount of output N of animal body is 426.7 × 10~4 t, which accounted for 22% of the total output N. And the loss of N during the feeding is tiny.4. In rural and urban family, the major input of N was food. And the N of plant food is more than that of animal food. But the N of animal food consumed by urban family is more than that by rural family. The amount of N of animal food consumed by urban family and rural family was 75.78 and 45.8 ×10~4 t respectively. The N of human feces was the major output in family system. The amount of N in living rubbish and human feces of rural family is more than that in urban family. The N surplus was assimilated by people. And the percentage is 15% of the total input N. |
