Studies On Controlling Nitrate Content Of Lettuce And Its Effect In Nutrient Solution Culture

In the experiment, the lettuce was used as experimental materials, adopted the way of nutrient solution culture to study controlling of nitrate content of lettuce and its effect with completely controlling nutrient and timed harvest, different growth period and harvest time, different concentrations of nutrient solution and controlling nitrogen, different nitrogen forms and proportions. The main results obtained were summary as followed: 1).difference among different nutrient formula was significant in nitrate content. The high and low sequence is: Japanese garden formula>Holland formula>YannongA formula>YannongB formula. The different nutrient solution formula matches with the corresponsive concentration can control nitrate content of lettuce effectively, enhance yield. Therefore, under the condition of not affecting the growth and yield, looking for the formula of the lower nitrate content is viable. 2).Nitrate content was different during whole growth. Nitrate content always appeared declining in mid-later period, but NRA appeared gradually increasing, then declining. NRA has the function of lowering nitrate content of lettuce in mid-later period. In a day, nitrate content is gradual declining, the trend changes slowly after 14.00 pm; NRA is increasing continuously from 8.00 am to 14.00 pm, then declining gradually. Therefore the harvest period can be put off properly.3).Within the proper range of nutrient solution concentrations, nitrate content went up along with the increasing of nutrient solution concentrations, NRA strengthened too. The nitrate content and NRA showed a positive correlation; but after stopping supplying nitrogen, they didn't show the relation. 4).The effect of different nitrogen forms and ratio on nitrate content in nutrient solution culture. NH₄⁺-N and urea can reduce nitrate content of lettuce, enhance yield, improve quality. It was found that suitable NH₄⁺-N : NO₃^--N(30 ∶ 70 , 50 ∶ 50)in nutrient solution is better than others treatments. 5).Nutrient solution had been replaced water before lettuce was reaped for a week, which can reduce effectively accumulation of nitrate in lettuce, moreover, the effect of the yields isn't apparent.