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Vegetables occupies a very important position in people's diet structure, green vegetables, pollution-free vegetables has been growing concern and attention. The greenhouse vegetable nitrate content is much higher than the open-air vegetable, reduce the nitrate content of vegetables to improve the quality of vegetables, to ensure human health. Vegetables nitrate accumulation and nitrogen fertilizer has a direct relationship, using conventional methods combined with isotope tracer technique to study the effect of nitrogen fertilizer on nitrate in vegetables and quality, nitrogen sources and vegetable nitrate accumulation and distribution relationships, The results showed that: 1. chemical nitrogen fertilizer on the basis of a 20% reduction by organic manure, fertilizer trace elements, application of nitrification inhibitors and urease inhibitors and other agronomic measures reduce the nitrate content of vegetables 2.93% -22.05% nitrite content of 9.09% -53.17%; summer vegetables in the process of accumulation of nitrate in vegetables accumulation peak as early as the winter vegetable, vegetables post-nitrate content than the growth period was significantly decreased; under the same conditions of nitrogen fertilizer, organic fertilizer with Shi trace elements, nitrification inhibitors and urease inhibitors and other agronomic measures can improve vegetables, vitamin C and soluble sugar content, and vegetables chlorophyll SPAD value did not change significantly. Chapter II of vegetables as a nitrate enrichment plant, nitrate distribution in the body stems greater than the leaves, stem nitrate content in leaves about 1.5 times, the distribution of VC in the vegetables than stem leaves vegetables, root and leaf nitrate reductase activity is much larger than the stems. The cumulative impact of different types of Nitrogen on Nitrate: sodium nitrate, followed by ammonium sulfate, urea and ammonium bicarbonate smaller than the Bureau of nitrate content of vegetables with high vitamin C content. Nitrate in the third chapter of vegetables from the stems from the soil, more than 80%, from fertilizers part less, only about 15%. Vegetables on soil nutrient requirements, particular emphasis on the reduction and control of the soil part of the nitrate in vegetable production, reduce the absorption of vegetables on soil nitrate, and thus achieve the purpose of reducing nitrate in vegetables. Application of urea fertilizer utilization rate reached 42.67%, residual soil nitrogen 17.01%, higher than the ammonium sulfate and sodium nitrate, urea loss rate of 40.32%, far less than 52.67% of the ammonium sulfate and sodium nitrate 54.15% This indicates that the application of urea is conducive to maintaining and improving of soil nitrogen reserves.
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