Mode Of Managing Nutrient Solution Based On N Use Efficiency For Lettuce(Lactuca Sativa L.)

In aeroponic cultivation the nutrient solution is an essential component to achieve good production results, and nitrogen is the main constituent element of the nutrient solution and essential element in plant nutrition, it is a key factor in the growth and development of vegetable crops. In this study, Italian lettuce (Lactuca sativa L.) as a research object, initial pH and mode of replacing the nutrient solution management as objectives, experiment cultivation conducted using the Japanese garden nutrient solution formulations. Among them, the nutrient solution initial pH values were set5,6and7, replacing the nutrient solution includes three modes: replacing all nutrient solution every10days, i.e. M1; replacing half of nutrient solution every10days, i.e. M2; adjust the EC keeping nutrient solution total salt content, i.e. M3. According to2factors and3levels full factorial experimental design test unit (Ti～T9), cultivation experiment period of30days, sampled once every10days, were taken nutrient solution concentration of ammonium nitrogen (NH4-N), nitrate nitrogen (NO3-N) and gross nitrogen (GN) for chemical analysis. After harvesting lettuce, were made lettuce yield statistic, nitrate (NO3-) content in leaves detection, and root morphology scanning, while based on the obtained data, calculate water use efficiency (WUE) and nitrogen use efficiency (NUE). The experiment shows that three mode of replacing the nutrient solution and three initial pH values and their interaction significantly influenced the fresh weight and dry matter of lettuce (P<0.05). The highest values of fresh weight (FW) and dry matter (DM) were recorded in the T5where there is an interaction between pH6and M2and the lowest FW and DM in T2with pH5and M2. The means of plant FW and DM inpH values were high for pH6, middle for pH7and low for pH5, with123.41g FW and14.3g DM,107.8g FW and10.5g DM, and88.64g FW and9.5g DM respectively. The consumption rate of nitrate nitrogen (NO3-N), ammonium nitrogen (NH4-N) and gross nitrogen (GN) was higher during stage1(0-10days), especially for the Mi. But the M3had a negative consumption rate in the third stage (21-30days), which indicated that the conversion of N forms was not only these two forms but also probably existed nitrite (NO2-N) and plants can absorb and use the new N forms, which influences the gross nitrogen (GN) of all process. The nitrate concentration levels obtained in lettuce leaves do not exceed the limits set by the European Union, where inpH=6and Mi, obtained the lowest NO3-content in leaves, and in nutrient solution concentration regulation using M3, in any initial pH, the NO3-content in leaves were highest, however, this regulation by nutrient concentration, WUE and NUE where highest. The experiment shows a positive relationship (P<0.05) between NUE and WUE with FW and DM. More higher the efficiency of water and nitrogen use, higher will be the fresh weight and dry matter. The different management modes is not significant influence on leaf chlorophyll index (P>0.05) which ranged from18.37to25.4SPAD units, but significantly affect lettuce root morphological development (P<0.05). Analysis shows that in the aeroponic lettuce cultivation, N of nutrient solution, influencing the biological root morphology, nutrients, water absorption and dry matter accumulation of lettuce.