Abstract
While the effluent pollutant loads of nitrogen, phosphorus, and COD from paddy fields are very important basic figures in a wide variety of environmental planning and research tasks, more reliable figures have been required. In this paper, the database of the pollutant load from paddy fields in Japan, established by the authors, is explained and the analytical results and future issues are presented. The database is based on the 72 references published since 1980s and it includes 467 data sets of the pollutant loads and information on the references, and investigation and farming conditions. The investigation of the irrigation season and the verification of the effects of the wide variety of improved farming methods during the irrigation season have been conducted in Japan. However, data for nonirrigation season and specific data obtained in paddy fields cultivated using variety of farming methods will be needed. The verification of the effects of the improved farming methods in the nonirrigation season and the development of the best management practices for the reduction of the pollutant load in the nonirrigation season are also required. The figures for phosphorus and COD adopted for the Seventh Total Water Pollutants Reduction Plan and the water conservation plan for selected lakes are much lower than the average values for by conventional farming methods available in the database. Therefore, the values for the Seventh Total Water Pollutants Reduction Plan will be revised referring to our database. The pollutant load from a paddy field cultivated by custom farming decreased with the decrease in the amount of fertilizer used. Thus, the recent data will be of great value. Other countries are facing a shortage of the data on pollutant loads in paddy fields. In the countries, there is a lack of experience in improving methods of farming to reduce the pollutant loads in paddy fields. Therefore, our database will be useful for other countries. The database is available on the web, and it is expected to contribute to future governmental and research activities.
