Monitoring of inorganic nitrogen levels in the surface and ground water of the Red River Delta, northern Vietnam

Concentrations of ammonium-nitrogen (N) and nitrate-N and the pH of the surface and ground water were monitored in three rural communes differing in topography, soil type, and cropping pattern in the central Red River Delta, northern Vietnam, at the end of the rainy season in 2002. Information on the amount of fertilizer N applied and the kind and number of livestock feeding was obtained through interviews of the farmers. The amount of fertilizer N annually applied by a farm household was around 400kg/ha in average and was a very high level compared to other Asian countries. The ammonium-N concentrations of the surface and ground water were relatively high and exceeded the Vietnamese water standard for purposes other than drinking use and for drinking use, respectively. Possible impacts of the topography of the communes on the ammonium-N concentration of the surface were suggested. The nitrate-N concentrations of both surface and ground water were generally lower than 0.4 mg/L with an exceptionally high value of 5 mg/L in the grey degraded soil area, and were always below the ammonium-N concentrations at the corresponding sites in the alluvial soil area, indicating the suppressed condition of nitrification in the soil and water. The low pH of the ground water measured at some sites in the grey degraded soil area was out of the Vietnamese water standard for drinking use.