The effect of different amounts of N-fertilizers on the nitrate accumulation in the edible parts of vegetables

Abstract

Eight important vegetables i.e. spinach, lettuce, celery, cabbage, parsley, leek, radish and cress were grown at low to high rates of nitrogen fertilization. Seven N-fertilizer treatments consist of 0, 100, 200, 300, 400, 500, and 600 N kg/ha conducted in Varamin in 1995 for spinach, lettuce, celery cabbage and on the other four vegetables the five treatment contained, i.e. 0, 100, 200, 300, and 400 N kg/ha carried out in Karaj region in 1996. At harvest time, two leaf samples were taken: one in the early morning and the other in the evening and nitrate content was measured by sulfosalicylic method. The results revealed that there was a positive relationship between the amount of N-fertilizer and nitrate accumulation. The maximum nitrate accumulation occured with 400 kg N/ha treatment. In these treatments, leaf samples taken in the evening, had less nitrate in comparison with the morning harvest. The results also revealed that the yields were increased up to 400 kg N/ha treatment significantly but additional N-fertilizers did not increased their yield may be due to the ammonium toxicity.