| In order to study the nitrate accumulation mechanism of vegetable and then make out some cultivated measures for low-nitrate vegetable, hydroponic culture experiments, pot experiments and field experiments were conducted to study the effects of N, K, P, Mo, different N fertilizers, different supplying periods and. different levels of N-fertilizer on the nitrate content of Swamp Cabbage. As the same time, the nitrate dynamic changing of different organs of Swamp Cabbage was examined as well. The results showed as follow:1. In hydroponic culture experiment, different N form ratio had a significant effect on the nitrate content of Swamp Cabbage.But in field experiment ,the nitrate content of Swamp Cabbages supplied different chemical N-fertilizer had no significant difference. Supplying organic fertilizer could markedly decrease the nitrate accumulation of Swamp Cabbage.2. Supplying approprate amount of K-fertilizer could significantly decrease the nitrate content of Swamp Cabbag , but deficiency or excess of K nutrient caused nitrate accumulation.3. P had no obvious influence on the nitrate accumulation of Swamp Cabbage when P hadn't become the limit factor of plant growing.4. Supplying appropriate amount of Mo could increase the nitrate reductive activity of Swamp Cabbage, decrease the nitrate accumulation. But excess of Mo would result in raplidly improving the nitrate content and seriously accumulating Fe, Cu, Mn, Zn in Swamp Cabbage, inducing poisoning symptom of plants.5. Analysing the nitrate dynamic changing of leaves, stems and roots of Swamp Cabbage,it could be known that the nitrate of Swamp Cabbage was mainly accumulated in stems and roots. Supplication of chemical N-fertilizer induced a large number of nitrate accumulation in stems and roots.6. In field experiments, different N fertilizers, different level of N fertilizers anddifferent periods of supplication all exerted very significant influences on nitrate concentration of Swamp Cabbage.The treatments supplied urea and the one supplied NaNOs had higher nitrate concentration than that one supplied organic fertilizer. But the treatment supplied urea had no obvious difference with that one supplied NaNOa in nitrate accumulation; The Swamp Cabbage supplied low level of N-fertilizer had lower nitrate content than medial and high level, but the nitrate content in Swamp Cabbage was not significant different between the medial and high level N fertilizer. The nitrate content of Swamp Cabbage supplied fertilizer 5 days prior to harvest was significantly higher than those supplied fertilizer 15 days or 25 days prior to harvest, but the difference of nitrate content between that supplied fertilizer 15 days and 25 days prior to harvest was not significant. |
