02341naa a2200181 a 450000100080000000500110000800800410001910000120006024501340007226000090020652015010021565000290171670000130174570000140175870000180177270000170179077303520180714651502005-04-28       2002    bl ---       0--  u    #d1 aITO, O.  aCase study on development of the sustainable agricultural system for various agro-ecosystems through assessment of nitrogen flow.  c2002  aImportance in the sustainability of agricultural systems has long been recognized in relation to maintaining and improving agricultural productivity in harmony with the surrounding environment. In many cases, however, the sustainability is discussed rather qualitatively, not quantitatively. This is mainly because of lack of measurable indicators to express the degree of the sustainability in the system. The nutrient is an essential element for the agricultural systems and the appropriate management of such nutrient should be one of the key points for sustainable development of the system. Moreover, the nutrient flow within the system can be quantified at a certain degree and the nutrient budget that is a consequence of balance between input and output may be closely related to sustainability. Optimization of nitrogen cycling in the farm community is considered to be an important aspect as nitrogen is a major nutrient to increase agricultural production. In this paper, a whole picture of the nitrogen cycle for agricultural production that was constructed based on data collected from agricultural statistics, research reports, study reports, field observation, interview with farmers and information from experts, will be presented with particular focus on three areas in the East and Southeast Asian countries such as Shandong provinve in China, Northeast Thailand, and Mekong Delta. The obtaned nitrogen budgest is also discussed in order to improve sustainability of the system.  aAgricultura Sustentável1 aYAGI, K.1 aHOSEN, Y.1 aMATSUMOTO, N.1 aWATANABE, T.  tIn: TAKEYA, H.; TANABE. T.; YAMAUCHI, A.; MAEDA, K.; CEDICOL, E. C. (Ed.). Sustainable agricultural system in Asia: strengthening human resource development program in universities. Nagoya: Graduate School of Bioagricultural Sciences: International Cooperation Center for Agricultural Education: Bioscience and Biotechnology Center, 2002. p.47-52.