Abstract
A method was proposed to assess the risk of nitrate pollution of groundwater by utilizing the nitrogen fertilization load (NF load), which is the amount of nitrogen not absorbed by the individual crop species form nitrogen applied as fertilizers and composts. The standard NF load was estimated from statistical data on the fertilizer application in Japan. This method follows : 1) The area of each crop in municipalities are collected from the statistics. The total NF load in each municipal is calculated by multiplying the area of each crop by the standard NF load. 2) The total NF loads are divided by the total areas of the municipalities to estimate the risk indicator of ground water pollution by nitrate with fertilized nitrogen. The applicability of the indicator was confirmed to have the good correlation (significant at p<0.01) with nitrate+nitrite-N levels in shallow wells in municipalities in Ibaraki Prefecture and Nagano Prefecture. 3) When the municipalities have considerable different annual rainfalls, total NF loads are divided by the products of (the total areas of the municipalities) and (the differences between annual rainfall and evapotranspiration). This indicator was confirmed to have a better correlation than the above indicator with nitrate+nitrite-N levels in shallow wells in municipalities in Nagano Prefecture.
