Effects Of Nutrient Solution Supply On The Growth And Nitrate Accumulation Of Lettuce

The effects of nutrient solution supply on the growth, nitrate accumulate and quality of lettuce (Lactuca sativa L.) were studied by means of water culture in this paper. The research includes four parts: The effect of different stop solution concentration supply times on lettuce before harvest; The effect of The effect of different N forms on lettuce; The effect of different solution concentration on lettuce. The results are as follows:1. Effects of four stopping nutrient solution times before harvest (0d;4d;8d;12d) on the lettuce (cv. Hongnong and Lvling) growth , nitrate accumulate, quality and mineral nutrient were investigated. The results showed that the times of stop the nutrition solution over 8 days, the fresh and dry weights of shoot, leaf s number , leaf length , leaf width and Shoot water content decreased gradually, whereas the fresh and dry weights of root, root/shoot ratio increased significantly. The times of stop the nutrition solution is 4 days, no effect significantly on growth of lettuce. The nitrate content and soluble sugar decreased significantly with increasing of times of stop the nutrition solution, whereas the nitrate reductase increasing significantly. When the times of stop the nutrition solution over 8 days, the soluble protein and vitamin C decreased significantly, whereas the times of stop the nutrition solution is 4 day, no effect significantly on the soluble protein and vitamin C of lettuce. N, P, K, Ca, Mg of shoot and root decreased significantly with increasing of times of stop the nutrition solution.2. Effect of different solution concentration in different stage (1s-1s-1s; 2s-1/2s-1s; 1s-2s-1/2s;1/2s-1s-2s) mean three nutrition solution concentration models (H-L-M; M-H-L; L-M-H) and the control on the lettuce (cv. Hongnong and Lvling) growth, nitrate accumulate, quality and mineral nutrient were investigated. The results showed that "M-H-L; L-M-H" made fresh weight and dry weight of shoot and root increase significantly, whereas "H-L-M" decrease significantly. The nitrate content of "M-H-L" decrease significantly, but the nitrate reductase increase significantly, whereas the nitrate content and the nitrate reductase all increase significantly. soluble sugar, soluble protein , vitamin C, N and P of "M-H-L; L-M-H" increase significantly, but K , Ca and Mg decreased significantly,whereas nutrition solution concentration models "H-L-M" was contrast with "M-H-L; L-M-H".3. Effects of four nitrogen forms (NO₃^-—N:NH4⁺—N were 100:0, 75:25, 50:50 and 0:100, respectively)on the lettuce (cv. Hongnong and Lvling) growth and the activity of protectiase enzymes were investigated. The results showed that the fresh and dryweights of shoot and root decreased with increasing of ammonium nitrogen form, leaf number, leaf length, leaf width and leaf water content also decreased significantly, whereas root/shoot ratio increased, difference between different treatments on the shoot growth was only significant ten days after transplanting. SOD and POD activities increased with increasing of ammonium nitrogen form. Different nitrogen forms had no significant influence on the MDA content 13 days within transplanting, but for the treatments of complete ammonium nitrogen and NO"3 — N:NH+4 — N(50:50), MDA content increased sharply 10 days after transplanting. The leaf nitrate content was the highest in the complete nitrate nitrogen treatment, and it decreased with increasing of ammonium nitrogen form, the contents of soluble sugar and soluble protein were the highest in the treatment of NO3"-N:NH4+-N(75:25).4. Effect of four nutrient solution concentration (l/4s, l/2s, Is, 2s) on the lettuce (cv. Hongnong and Lvling) growth, nitrate accumulate, quality, mineral nutrient and the activity of protectiase enzymes were investigated. l/2s made the fresh and dry weights of shoot and root, leafs number, leaf length, leaf width and Shoot water content increasing gradually. The rest are Is, l/4s and 2s. The nitrate content and the chlorophyll content increasing significantly with increasing of the nutrition solution concentration. TTie SOD activities of 2s changed low into high from the seedling period to harvest period. The MDA content of 2s was more significantly than the control, whereas the MDA content l/2s was less than the control. The nitrate content, soluble sugar, soluble protein and vitamin C of lettuce of 2s increasing significantly, whereas l/2s decreased significantly. N, P, K, Ca of l/2s in shoot and root increasing significantly, Mg of shoot and root decreased significantly with increasing of the nutrition solution concentration.