Effect Of Different Nitrogen Levels On The Content Of Nitrate In Several Leafy Vegetables Under Hydroponics Cultivate

This paper reached the characteristics of the nitrate content of different type's leafy vegetables which were hydroponics cultivated under different nitrogen level and equilibrium fertilizer (N, P, and K) as well as reached the characteristics of nitrate accumulation of leafy vegetable under storage and cooking. It offers theory basis for leafy vegetables safe production and theory references for safe consuming of leafy vegetables. The main conclusions were as follows:1 The nitrate content of three leafy vegetables under different nitrogen level was: Chinese cabbage> Spinach> lettuce. Chinese cabbage nitrate content showed that: petiole (stem)> leaves> root; Spinach nitrate content showed that: root> petiole> leaves. When lettuce nitrogen concentrations≤15mmol/L, nitrate content showed that: petiole> Root> leaves; When nitrogen concentrations≥20mmol/L, nitrate content showed that: petiole, root> leaves.2 With the increase of nitrogen concentration, the biomass of four varieties of Chinese cabbage have increased. The nitrate content of four varieties of Chinese cabbage showed that: shanghaiqing> Siyueman> Heiyoubaicai> Wuyueman. The nitrate content of various organs had difference in the different varieties of Chinese cabbage. The nitrate content of leaves and petioles are showed that: Shanghaiqing> Siyueman> Heiyoubaicai> Wuyueman. The nitrate content of root showed that: Siyueman > Wuyueman > Shanghaiqing > Heiyoubaicai. The nitrate reductive activity (NRA) was growing with the increase of nitrogen concentration of Chinese cabbage, but tow Chinese cabbage, NRA has no significant difference.3 The biomass of two kinds of lettuce was increasing with the nitrogen increased. The biomass between the different nitrogen concentrations had a little difference. The nitrate content of two kinds of lettuce increased with the concentration of nitrogen increased. The nitrate content of Lettuce petiole had obvious differences in the different nitrogen treatment. Nitrate content of lettuce roots were all higher in different nitrogen concentration. The nitrate concentration of Hydroponics was: N4> N1> N3> N2. The nitrate reductive activity of two kinds of lettuce has difference.4 The nitrate content of Chinese cabbage was significantly different under equilibrium fertilization treatment. When nutrient share of Hydroponics of N: P2O5: K2O for 1:0.5:1.25, The nitrate content of Chinese cabbage reached the highest value 1824.86mg/kg. The nitrate content of Chinese cabbage organ was: petiole (stem)> leaves> root. The nitrate content of Chinese cabbage increased as treatment time increased which showing a gradually increasing trend.5 Under room and refrigerate temperature, nitrate content reduced as storage time extended in the fresh and blanching of Chinese cabbage. The nitrate content reduced 16.76-79.16% after 48 hours. The nitrate content of Chinese cabbage refrigerated was higher 21.77-234.5% than that of room temperature storage. Under cooking treatment, the nitrate content of Chinese cabbage reduced about 51.58%, but nitrite content increased 391%. The nitrite content of Chinese cabbage had positive correlation with the nitrogen concentration.