Spatio-temporal change of nitrate pollution of groundwater in lowland agricultural landscape in Batac, Ilocos Norte, Philippines
2005
Fariñas, A. R.
The spatio-temporal change of nitrate levels in shallow groundwater wells of lowland rice field planted to rice in the wet season and upland crops such as eggplant, sweet pepper and corn during the dry season was assessed in 2004. The 13 farmer-cooperators applied as much as 122kg N/ha for rice and as much as 450kg N/ha for sweet pepper. Furrow irrigation was done on upland crops. Temporal assessment was done for the monthly variation of nitrate levels in the rainfed lowland rice and upland cropping seasons. The Inverse Desistance Weighted (IDW) interpolation method was used the assess the monthly spatial variation of ground water nitrate levels. It depicted high concentration of nitrate in areas where spatial data of excessive fertilizer application were found. The levels of nitrogen fertilizer application were significantly correlated with mean monthly groundwater nitrate levels in the upland crops specifically for eggplant. The mean monthly groundwater nitrate levels during each cropping were generally low and did not exceed the critical level of 10 ppm except for two wells. Planting of corn as a forage crop after eggplant reduced the level of soil nitrate. Nitrate pollution of groundwater can be minimized by planting corn forage crop after eggplant to utilize residual soil nitrate. Monitoring of the groundwater nitrate must be continued for the sake of public awareness and for the purpose of adapting mitigating measures to reduce environmental impact.
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