Abstract:
This paper compares the effects of adding fertilizer in nitrate pollution of
groundwater in the Udunuwara area in Sri Lanka and the Shiroishi Plain in Japan.
Excessive application of nitrogen fertilizers to soils contributes to contamination
of groundwater by nitrates. As nitrate is one of the most identified contaminant in
groundwater several environmental protection agencies maximum contamination
level for nitrate is 10 mg/l as NO3
-N. The problem becomes severe in rural areas
where people depend entirely on dug wells in the shallow groundwater table for
their drinking water supply. Several locations were selected from the Udunuwara
area of Sri Lanka for the detailed study. Nineteen shallow dug wells and 4 deep tube
wells were selected for water sampling beginning of January to March 1998.
Shiroishi Plain in Japan reclaimed from the Ariake Sea has a soil layer consisting of
Ariake clay. The total 82 drug wells of average depth 1.5 m had been drilled around
the area. Sample were collected in December 2000 and continued for one year
around. Nitrate concentration in groundwater was measured by Cadmium reduction
method.
The results showed a varying nitrate distribution pattern compared to that the
Udunuwara area. The effect of fertilizer application on groundwater depends on
soil type, fertilizer type and amount used, crop type and climatic condition. The
highly permeable soil around Udunuwara area showed that shallow groundwater
is highly vulnerable for nitrate than the poorly drained soil of the Shiroishi Plain in
Japan. As the people living in Shiroishi Plain use deep groundwater for domestic
purposes, drinking water is safe (less than Maximum Contaminated Level for nitrate
in drinking water for Japan-10 mg/l as NO3
-N) as far as the nitrate contamination is
concerned. The results of these studies suggest that applying the correct rate of N
fertilizer at the optimum time would have a substantial effect on reducing nitrate-N
losses.
