Effects Of Different Nitrogen Concentration And Form On Nitrate In Radish Leaf

In order to study the nitrate accumulation mechanism of vegetable and then make out some cultivated measures for low-nitrate vegetable, hydroponic culture experiments were conducted to study the effects of different genotypes, different levels of N-fertilizer, different supplying periods and different N form ratio on the nitrate content of radish. The results showed as follow:1. The genotypic differences of nitrate content in 36 leaf radish cultivars were studied in this experiments. The results indicated that there were significant differences of nitrate content among these cultivars, the difference between the highest and the lowest amounts to 900g/gFW. Through this experiment, we selected 3 cultivars with higher nitrate content: "qinyedongchunwang", "xiakangsishitian", "maer" and 3 lower ones: "liushizao", "hongpimazhuangluobo", "dahongyanzhiluobo"2. Studies of two-step selection on nitrate concentration 0, 4, 8, 12 , 16, 20mmol/Land 1, 2,. 3 , 4 , 5mmol/L were applied on 5 cultivars:"duanyeshisan" , "qingyedongchunwang" , "maer" , "liushizao"and"dahongyanzhi". The results indicated that nitrate content and yield increased remarkably with N concentration rising in a certain rage, but then go up slowly or stop or even go down when the N fertilizer surpass their limitation. From this experiment, the treatment of N4 was better for radish to achieve high yield and relatively low nitrate content.3. The treatments being deprived of N within 3 days before harvest showed significant decrease of nitrate content, especially within 1 day before harvest. Compared with continuous N supply, the sharpest reduction of nitrate occurs in Nl treatment. In N4 treatment, the proportion of decrease of nitrate in leaves of "maer" was second only to that of Nl treatment, is 86.3%~99% and "liushizao"was 87.8%~97.9%.For the nitrate content of different plant tissue, leaves and roots reduced a little larger than shoots and petiole.4. With the decreasing ratio of nitrate/ammonium, Vc con tent N nitrate content, activity of nitrate reductase and yield all declined except protein, while protein shows an increasing pattern, when the ratio of nitrate/ammonium in nutrient solution reduced from 100/0 to 75/25, nitrate content dropped sharply, and then slowly. In consideration of yield and the content of nitrate in radish, the optimal ratio of NO3-/NH4+ was recommended to be 75/25 for "dahongyanzhi", "maer", and "liushizao", 50/50 for "qingyedongchunwang".5. With the decreasing of ratio of nitrate/ Urea, nitrate content , activity of nitrate reductase and biomass production declined, but variations were not the same pattern.. the greatest reduction of nitrate was shown when the ratio of nitrate/ Urea in nutrient solution varies from 100/0 to 25/75. Results from this experiment showed that optimal ratio of nitrate/Urea , 25/75 for "dahongyanzhi" in this case, were essential, from a comprehensive view, to achieve high yield and relatively low nitrate content.