RESUMO
We investigated the content of NO<SUB>3</SUB>-N in the well water of the eastern, middle and nothern districts of Nagano Prefecture. The NO<SUB>3</SUB>-N content seasonally changes and takes on the pattern of a high in summer and a low in winter.<BR>Rain is considered to dilute the contaminated well water, but it lets NO<SUB>3</SUB>-N flow from the soil into the.well water, when the rain is poured by a typhoon. As a result, a high content of NO<SUB>3</SUB>-N is measured in the well water.<BR>The water sample of 25 out of 85 wells in Matsukawa Town exceeded the tolerance level of NO<SUB>3</SUB>-N (10 ppm, but 44.3 ppm in terms of NO<SUB>3</SUB><SUP>-</SUP>).<BR>By crop area, the amount of NO<SUB>3</SUB>-N was highest in the fruitgrowing area, which was followed in order of the vegetable-growing area, the flower-growing and the rice planting area.<BR>We consider that the contamination of well water is caused both by chemical fertilizers and the less absorbility of the soil.