Nitrogen fertilization and nitrate pollution in groundwater in Japan: Present status and measures for sustainable agriculture

During the last two decades, nitrate nitrogen (NO3-N) concentrations in groundwater in Japan have increased steadily due to the development of intensive agriculture. In some areas, they have reached or even exceeded the unacceptable level for drinking water, 10 mg l(-1). In 2000, the Environment Agency showed that 5.6% (173 of 3,374) tested wells and 4.7% (64 of 1,362) wells used for drinking water exceeded the standard level in 1999. The highest value of NO3-N in the wells was 100 mg l(-1). Many researches have shown that NO3-N pollution of groundwater was widely observed in Japan, except the paddy field regions. Farming practices in Kagamigahara city of Gifu prefecture have been typical ones for reducing NO3-N pollution in groundwater. In the east district of the city, NO3-N concentration was low in 1966, but reached 27.5 mg l(-1) in June, 1974. The farmers in this district began to reduce the nitrogen fertilizers in carrot cultivation, going from 256 kg N ha(-1) in 1970 to 153 kg N ha(-1) in 1991. The use of controlled release fertilizer increased fertilizer-nitrogen efficiency compared with common compound fertilizer and NO3-N concentration in the groundwater began to decrease steadily. It was discussed that in order to decrease the NO3-N pollution of groundwater, it is necessary to refocus not only agricultural technology but also agricultural policy, toward sustainable agriculture and rural development.