Originating from a desire to reduce production costs, and find out suitable types of hydroponic nutrient solution for different types of leaf vegetables, a study was conducted on 4 types of vegetables including lettuce, Chinese cabbage, celery and water morning glory with three formula of nutrient solution. Two solutions by Hanoi Fruit and Vegetable Research Institute was studied in comparison with the control solution by the Institute of Agricultural Biology (Hanoi University of Agriculture). The results show that the nutrient solution by the Institute of Agricultural Biology (Hanoi University of Agriculture), nutrient solution VRQl by Hanoi Fruit and Vegetable Research Institute are suitable for lettuce, Chinese cabbage and celery. After 20 days grown in this solution, the yield of lettuce reached 35.46 and 35.28 quintal/l000 m2 respectively
the yield of Chinese cabbage reached 38.52 and 38.94 quintal/1000 m2 respectively. After 30 days grown in this solution, the yield of celery reached 46.25 and 46.06 quintal/1000 m2 respectively. Nutrient solution VRQ2 is suitable for water morning glory, the yield of different picking times ranged from 44.56 to 63.52 quintal/1000 m2. All three nutrient solutions ensured the proportion of nitrates, lead and cadmium in vegetables is much lower than the permitted proportion. The proportion of nitrate in fresh lettuce is from 243 to 343 mg/100 kg, in fresh Chinese cabbage is from 285 to 342 mg/100 kg. The proportion of lead in fresh lettuce is from 0.028 to 0.053 mg/100 kg, in fresh Chinese cabbage is from 0.045 to 0.062 mg/100 kg. The proportion of cadmium in fresh lettuce is from 0.005 to 0.009 mg/100 kg and in fresh Chinese cabbage is from 0.004 to 0.008 mg/l00 kg.