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Nitrogen (N) leaching in vegetable fields from December 2002 to May 2003 with equal dressings of total N for asequential rotation of Chinese flat cabbage (Brassica chinensis L. var. rosularis) and lettuce (Lactuca sativa L.) in asuburban major vegetable production base of Shanghai were examined using the lysimeter method to provide a scientificbasis for rational utilization of nitrogen fertilizers so as to prevent nitrogen pollution of water resources. Results showedthat leached N consisted mainly of nitrate N, which accounted for up to more than 90% of the total N loss and couldcontribute to groundwater pollution. Data also showed that by partly substituting chemical N (30%) in a basal dressingwith equivalent N of refined organic fertilizer in the Chinese flat cabbage field, 64.5% of the leached nitrate N was reduced,while in the lettuce (Lactuca sativa L.) field, substituting 1/2 of the chemical N in a basal dressing and 1/3 of the chemicalN in a top dressing with equivalent N of refined organic fertilizers reduced 46.6% of the leached nitrate N. In the two-year sequential rotation system of Chinese flat cabbage and lettuce, nitrate-N leaching in the treatment with the highestamount of chemical fertilizer was up to 46.55 kg ha-1, while treatment plots with the highest amount of organic fertilizerhad only 17.58 kg ha-1. Thus, partly substituting refined organic fertilizer for chemical nitrogen in the first two seasonshas a great advantage of reducing nitrate-N leaching.
Nitrogen (N) leaching in vegetable fields from December 2002 to May 2003 with equal dressings of total N for asequential rotation of Chinese flat cabbage (Brassica chinensis L. var. Rosularis) and lettuce (Lactuca sativa L.) in asuburban major vegetable production base of Shanghai were examined using the lysimeter method to provide a scientific basis for rational utilization of nitrogen fertilizers so as to prevent nitrogen pollution of water resources. Results showed that leached N consisted mainly of nitrate N, which accounted for up to more than 90% of the total Data also showed that by partly substituting chemical N (30%) in a basal dressing with equivalent N of refined organic fertilizer in the Chinese flat cabbage field, 64.5% of the leached nitrate N was reduced, while in the lettuce (Lactuca sativa L.) field, substituting 1/2 of the chemical N in a basal dressing and 1/3 of the chemical N in a top dressing with an equivalent N of ref In the two-year sequential rotation system of Chinese flat cabbage and lettuce, nitrate-N leaching in the treatment with the highestamount of chemical fertilizer was up to 46.55 kg ha-1, while treatment plots with the highest amount of organic fertilizer only only 17.58 kg ha-1. Thus, partly substituting refined organic fertilizer for chemical nitrogen in the first two seasons has a great advantage of reducing nitrate-leaching.