Abstract: Forms and contents of N pollutants in groundwater in a typical small watershed in the hilly area of the Central Sichuan Basin were monitored for a year.Results show that nitrate was the main form of nitrogen in groundwater in the watershed.The content of nitrate-nitrogen in 54.5% of the monitored wells was found above 10 mg·L^-1（drinking water standard of WHO）,and 27.3% approaching 10 mg·L^-1,suggesting that nitrate pollution had occurred in a large area in the hilly region of the Central Sichuan Basin.Land use is the main contributor of NO₃^--N content in the groundwater,and precipitation and well depth are also affecting factors.In slope cropland of purple soil,nitrate accumulated in the plow layer moving down into subsurface flow could be the major source of the higher content of nitrate in the groundwater.

Key words: purple soil, groundwater, nitrate, pollution