Abstract: During 3 consecutive years (1999-2001), a field experiment was conducted in an intensively irrigated vegetable soil in Northern China. The main objective was to study leached nitrate (NO3--N) characteristics in vegetable field under traditional and improved water and nitrogen fertilizer management practices during vegetable growing seasons. The soil water content, soil water potential and extract of the soil solution were determined by a combination of TDR (time domain reflectometry) probe, tensiometers and ceramic suction cups. The results showed that the amount of nitrate leached decreased because water drainage was reduced when applied water was reduced. Cumulative leached NO3--N amount under traditional water treatment was 4.4 times and 4.5 times of that of improved in traditional and improved nitrogen fertilizer application management. When nitrogen fertilizer applied was reduced the amounts of leached nitrate also decreased obviously. Cumulative leached nitrate amount under improved nitrogen fertilizer management was 20% and 19% of that of traditional management in traditional and improved water treatments, respectively. The amounts of nitrogen fertilizer applied were the main factor affecting nitrate concentration in soil solution at the depth of 90 cm in soil profile. Nitrate concentration in soil solution at the depth of 90 cm under traditional nitrogen fertilizer management was higher than that of improved nitrogen fertilizer management. In the whole experiment the amount of nitrate leached was 549 kg·ha-1, which was 27% of the nitrogen applied under traditional water and nitrogen fertilizer management practices and nitrate leaching amount was 24 kg·ha-1, which was 5% of the nitrogen applied under improved water and nitrogen fertilizer management practices. Improved water and N-fertilizer management practices greatly decreased nitrate leaching without reducing vegetable yield.

Key words: Vegetable field, Water drainage, Nitrate leaching, Vegetable yield