Study On The Effect Of Slow-Release Nitrogen Fertilizers On Fertilizer Efficiency And Nitrate Accumulation In Different Vegetables

Slow-release nitrogen fertilizer is identified as the substitute product of the 21 century in fertilizer field. Compared with conventional fertilizer, Slow-release nitrogen fertilizer can effectively increase vegetable yield and nitrogen utilization efficiency, improve economic benefit, decrease nitrate content of vegetable and reduce environmental pollution. This study was to solve problems of decreased nitrogen utilization efficiency and exceeded criterions of vegetable nitrate content because of excessive fertilization, and to make research and development of new-style slow-release nitrogen fertilizers which could increase nitrogen utilization efficiency, ensure high-quality and high-yield of vegetable, and mitigate environmental pollution. It was very important to develop Chinese agriculture and pollution-free vegetable.Choosing two self-made slow-release nitrogen fertilizers, we investigated the fertilizer efficiency of slow-release nitrogen fertilizers on four vegetables (Spinach, Cherry-radish, Chrysanthemum and Leaf-used lettuce) and nitrate content of different vegetables with pot experiments and chemical analysis. The aim was to optimize fertilizer configuration, screen out optimal fertilizing amount and tolerated dose of fertilization in vegetables, increase nitrogen utilization efficiency effectively, decrease nitrate content to adapt vegetables to the criterion of safe food production, and provide data for exploring and spreading slow-release nitrogen fertilizers.Through analyzing yield of different vegetables, nitrogen utilization efficiency and nitrate content, this study was conducted on the two new-style slow-release nitrogen fertilizers and conventional urea under different nitrogen levels. The results showed that:1. In the condition of the equal weight nitrogen input, the slow-release nitrogen fertilizer I provided the highest yield of all vegetables. Compared with conventional urea, the slow-release nitrogen fertilizer I could increase four vegetables yields (Spinach, Cherry-radish, Chrysanthemum and Leaf-lettuce) respectively 75.85%, 60.12%, 273.45% and 123.43%, and the slow-release nitrogen fertilizer II could increase four vegetables yields (Spinach, Cherry-radish, Chrysanthemum and Leaf-lettuce) respectively 24.35%,27.40 %,63.24 % and 25.76 %. Under different nitrogen levels, vegetable yield was heightened at the beginning and then depressed. Four vegetables yields were the highest when applying N₂ level. And optimal fertilizing amounts of the slow-release nitrogen fertilizer I , the slow-release nitrogen fertilizer II and conventional urea were 0.49g N/pot (equivalent to the fertilization amount 29kg/667m²), 0.50gN/pot (equivalent to the fertilization amount 30kg/667m²) and 0.51g N/pot equivalent to the fertilization amount 31 kg/667m²) respectively.2. Under different nitrogen levels, the effect of slow-release nitrogen fertilizers on the nitrogen utilization efficiency was investigated, and the results showed that, slow-release nitrogen fertilizers could meet nutrient demand of the former two vegetables. Compared with applying conventional urea, applying the slow-release nitrogen fertilizer I and the slow-release nitrogen fertilizer II could improve the nitrogen utilization efficiency 13% and 12% respectively, and the highest nitrogen utilization efficiency was 55.09%. When cropping Chrysanthemum, the nitrogen utilization efficiency of urea was only 3.10%, and the slow-release nitrogen fertilizer I and the slow-release nitrogen fertilizer II were 11.96% and 6.08% respectively. When cropping Leaf-used lettuce, the nitrogen utilization efficiency of the slow-release nitrogen fertilizer I was over zero under N₁ and N₂ levels, and the nitrogen utilization efficiency of the slow-release nitrogen fertilizer II and urea were below zero. It indicated that there was no nitrogen to be absorbed. Through analyzing cumulated nitrogen utilization efficiency of the three fertilizers on four vegetables, it showed that the highest cumulated nitrogen utilization efficiencies was the slow-release nitrogen fertilizer I , following the slow-release nitrogen fertilizer II and urea, and the highest was 98.75%.3. Slow-release nitrogen fertilizers were able to decrease nitrate content of vegetables. With the increasing fertilization, the nitrate content of vegetables increased gradually among all treatments. And it represented significantly or very significantly positive correlation. Compared with applying urea, applying slow-release nitrogen fertilizers could reduce nitrate content of vegetables 57.77% and 37.10% respectively, especially in the former two vegetables efficiently. Nitrate content of slow-release nitrogen fertilizers was higher than urea during cropping Chrysanthemum and Leaf-used lettuce. Nitrate content of slow-release nitrogen fertilizer treatments didn't exceed 1440mg/kg (national band third criterion) in spinach treatment. When fertilizing amount exceeded 0.59g N/pot, nitrate content of urea treatment exceeded national band third criterion. Combined with vegetable yield, it could be concluded that fertilizing tolerated dose of slow-release nitrogen fertilizers and urea was the optimal fertilizing amount.4. Slow-release nitrogen fertilizers could increase vegetable yield and improve economic benefit. The remarkable treatment was N₂ level of slow-release nitrogen fertilizer I. The ratio of output/input of this treatment firstly increased and then depressed gradually with the increasing fertilization, and the highest ratio of output/input is Cherry-radish of slow-release nitrogen fertilizer I under N₂ level. 5. Under different nitrogen levels, soil alkali-hydrolysable nitrogen content of slow-release nitrogen fertilizer treatments was lower than urea treatment during the former two vegetables, but higher than urea treatment during the later two vegetables. With the time, the release curves of self-made slow-release nitrogen fertilizers were relatively relaxative, and the nutrient-releasing of slow-release nitrogen fertilizers was higher than urea during the later vegetables. Slow-release nitrogen fertilizers could provide enough nutrient for vegetables, which could mitigate contradiction between nutrient-supplying of fertilizers and fertilizer requirement rules of vegetables.All in all, the fertilization amount of 0.49g N/pot (equivalent to the fertilization amount 29kg/667m²) of the slow-release nitrogen fertilizer I was the optimal fertilizing amount and the tolerated dose, which could increase vegetable yield and nitrogen utilization efficiency, decrease nitrate content and enhance economic benefit to provide scientific guidance for future researches of slow-release nitrogen fertilizers.