Research On Influencing Factors Of Nitrogen Utilization Characteristics For Aeroponics Lettuce

In production,aeroponics is the best method of soilless cultivation to solve the contradiction between water and air.This method saves water and fertilizer,reduces plant diseases and insect damage,and increases production.It will be used to produce safer green vegetables in the future.To increase the leaf vegetables production,nitrogen supplyment still is given priority to nitrate nitrogen currently,but that increases the cost,results in the excessive levels of nitrate in vegetables and it is difficult to guarantee nitrogen utilization efficiency during production.Lettuce was selected as a subject because it was widely grown in soilless cultivation.In all experiments in this research,the semi-spray culture device is as the test equipment,and the Japanese garden formula is as the basic nutrient solution formula.This paper researched the effects of single factors(lettuce varieties,growth stages,ammonium/nitrate ratio and light intensity)and multivariate interaction on nitrogen utilization characteristics.Through the detection and analysis of nitrogen utilization efficiency,growth and quality indexs,and photosynthetic physiological indexes,the effect mechanism of various factors on nitrogen utilization characteristics was discussed,and the following results were obtained.(1)The effecting of lettuce varieties and growth stages.With American Grang Rapids TER lettuce,Italy Lettuce and Emperor Lettuce as test materials,lettuce varieties were studied on nitrogen utilization characteristics.Final test results showed that,Italian Lettuce had the best nitrogen utilization characteristics,so it was selected as the following test materials.At different growth stages(1-10d,11-20d and 21-30d),crop nutrient uptake efficiency appeared quite different and the maximum value appeared in the second growth stage,significant differences of photosynthetic indexes were also found in different growth stages.(2)The effecting of single environmental factor.With Italy lettuce as the research subject,ammonium/nitrate ratio and light intensity were respectively selected as the represents of the nutritional and physical environmental factors in order to research the effects on nitrogen utilization characteristics.Under the conditions of the mean values of temperature,humidity and natural light intensity were respectively 17.74℃,55.61%and 19.40KLux,results showed that,①aeroponics lettuce,ammonium/nitrate ratio of 25:75,had the best nitrogen utilization characteristics and the lower level of nitrate accumulation in leaves(2373.56mg·kg-1).Nitrogen production efficiency and root activity were extremely significant positive correlated(r=0.993,P=0.001),total dry weight was influenced by SPAD obviously(r=0.989,P=0.001),it inferred that ammonium/nitrate ratio by root activity affected the uptake and utilization ability of nitrogen,thereby affecting photosynthesis and material synthesis.②When the average light intensity is less than 19.40KLux,the stronger the light,the higher nitrogen utilization efficiency.So,filling light can significantly improve the yields and quality of crops when the average light intensity is below 19.40KLux.Total dry weight was most affected by net photosynthetic rate(r=0.998,P=0.002),nitrogen production efficiency and the root surface area were extremely significant positive correlated(r=0.994,P=0.006),nitrate absorption rate and net photosynthetic rate were extremely significant positive correlated(r=0.982,P=0.018),it inferred that light conditions by photosynthesis affected the uptake and utilization of nitrogen,thereby affecting crops growth.(3)The effecting of multivariate interaction.With Italy Lettuce as the research subject,the test set three factors(lighting intensity,growth stages and ammonium/nitrate ratio)and three levels using Box-Behnken central composite design,and then regression analysis using the quadratic response surface methodology.Under the conditions of the mean values of temperature,humidity and natural light intensity were respectively 30.87℃,39.57%and 45.42Klux,the results showed that,when the average light intensity is between 11.46KLux and 45.42KLux,with the increasing of light intensity,the root/shoot ratio and leaf nitrate accumulation rised after reducing first,other nitrogen utilization characteristics indexs all first increased and then decreased,crops produced light inhibition phenomena under natural light of 45.42KLux.Therefore,the appropriate shade is conducive to crops growth.The contribution rate of three factors on the effecting of nitrogen utilization characteristics:light intensity>growth stage>ammonium/nitrate ratio.The interaction of light intensity and growth stage affects nitrogen absorption rate most significantly,the interaction of growth stage and ammonium/nitrate ratio affects root activity most significantly,the interaction of light intensity and ammonium/nitrate ratio affects photosynthesis most significantly.The environmental conditions of light intensity of(32.5+2.5)KLux and ammonium/nitrate ratio of(52.5+2.5)%are more conducive to Italy Lettuce growth.To improve the quality of vegetables,ammonium/nitrate ratio should be close to 1:1.