Groundwater: an endangered resource from intensive rice-based cropping systems
2000
Castaneda, A.R. | Bucao, D.S. | Bouman, B.A.M. | To Phuc Tuong (International Rice Research Inst., Los Banos, Laguna (Philippines). Agronomy, Plant Physiology, Agroecology and Soil and Water Sciences Div.)
Drinking water in rural areas is often drawn from groundwater through shallow tube-wells. Intensive rice-based cropping systems are practised in some areas where farmers plant rice during the wet season and upland crops during the dry season. The upland crops are frequently irrigated utilizing groundwater and received heavy applications of chemical inputs, which may contaminate the aquifer. Nitrate contamination of shallow groundwater under intensive rice-upland cropping systems was monitored across Ilocos Norte [Philippines] in 1997-99. The selected measurement sites, represent major upland crops, such as sweet pepper, garlic, tobacco, tomato, and maize. For comparison, rice-rice and rice-fallow systems were also monitored. Groundwater samples were collected from domestic tube-wells in residential areas and from installed field tube-wells (used for irrigation) within the boundaries of the cropped areas. Shallow groundwater under the rice-sweet pepper system had the highest nitrate-N concentrations of about 7-11 ppm. Second was groundwater under rice-garlic and rice-tomato with 4-5 ppm nitrate-N. The nitrate-N concentration under rice-rice and rice-fallow systems were almost equal at about 1 ppm. Fertilizer N application was 450 kg N/ha in rice-sweet pepper, 250-350 kg N/ha in rice-garlic and rice-tomato, 100 kg N/ha in rice-fallow and 200 kg N/ha in rice-rice systems. Most nitrate-N concentrations found in rice-pepper exceeded the maximum permissible level of 10 ppm for drinking water. It is important to find technologies that minimize nitrate pollution of groundwater under this cropping pattern
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