Effects Of Various Aeroponic Nozzles(Droplet Sizes),Nutrient Solution Spraying Times And Spraying Intervals On Physciochemical Properties Of The Atomized Nutrient Solution And Growth Of Lettuce Plants

At present,the use of less resources to increase production is a hot issue in the field of agricultural engineering,and aeroponics has the advantage of extreme water saving and fertilizer saving,and is an effective method to solve this problem.In the current research on aeroponics technology,there are four key problems that have not been solved:?1?How does the physicochemical properties of the nutrient solution change after it is atomized into the aeroponic??2?How does the key operating parameters of the atomizer?nutrient fog size,spray time and spray interval?affect crop growth??3?What is the relationship between growth,quality and nutrient uptake parameters of the aeroponically cultivated plants and the key working parameters of the aeroponics??4?What are the optimal parameters for aeroponics technology?The research in this thesis attempts to answer and solve the above four key issues.So,the main work of this thesis is as follows:1.Design of the and development of the aeroponic cultivation systemTo achieve the above goal,firstly,an air-assisted electrostatic atomization nozzle was designed for atomizing the nutrient solution into the aeroponic system.In an aeroponic system,the nozzle atomized nutrient solution droplet size is one of the most important factors.No single study had intensely focused and discussed the selection of the suitable aeroponic atomization nozzle.Moreover,in practical applications of the aeroponic system,mostly garden sprinkler-type fluid atomization nozzles are used.In order to increase droplet adhering on roots,an air-assisted electrostatic sprayer was proposed and designed.The air-assisted electrostatic sprayers can produce the droplets smaller than those produced by conventional or hydraulic sprayers.Secondly,eight different aeroponic systems were developed.Moreover,proposed systems were developed by using four kinds of nozzles?ultrasonic nozzle,air-assisted nozzle,air-assisted electrostatic nozzle,and centrifugal atomizing nozzle?.Three kinds of nozzles?ultrasonic nozzle,air-assisted nozzle,and air-assisted electrostatic nozzle?were newly designed,and the centrifugal atomizing nozzles were purchased from the market.In addition,the droplet sizes measuring test of the selected aeroponic nozzles were conducted.The average droplet sizes of the air-assisted nozzle,air-assisted electrostatic nozzle,centrifugal atomizing nozzle,and ultrasonic nozzle were D_av=23.281?m,D_av=17.199?m,D_av=46.386?m,and D_av=3.451?m,respectively.2.Effects of different nozzles,nutrient solution spraying times and nutrient solution spraying intervals on physiochemical properties of the atomized nutrient solutionIn order to study the effects of different nozzles,nutrient solution spraying times and nutrient solution spraying intervals on the physiochemical properties?EC?Electrical conductivity?,pH,DO?Dissolved oxygen?and T?Temperature??of the atomized nutrient solution,two different experiments were conducted by selecting Yamazaki nutrient solution?YNS?and South China Agricultural leafy vegetable B nutrient solution?SCAULVFB?as test nutrient solution.Firstly,the effects of ultrasonic atomization frequencies on the physical and chemical properties of nutrient solution after atomization were studied.The ultrasonic nozzles?f?,nutrient solution spraying times?T₁?,and nutrient solution spraying intervals?T₂?were selected as test influencing factors to determine the effects on the EC and pH values of the atomized YNS.The nutrient solution spraying times and nutrient solution spraying intervals were used as quantitative factors with 12 levels?10,20,30,40,50,60,70,80,90,100,110,and 120 min,respectively?,and the ultrasonic nozzle atomization frequencies were taken as qualitative factors with 3 different atomization frequencies?f₁=28 kHz,f₂=107 kHz,and f₃=1.7 MHz?.The test factors level arrangement was set by adopting the Uniform design?UD?method U₁₂?12²×1³?,and the regression analysis test?p<0.05?was performed to assess the effects of the test influencing factors on the EC and pH values of the YNS.Based on the test results,the prediction models^*were established to estimate the effects of the aeroponic working factors on the atomized YNS.^*??EC=-304.75-0.2365T₁+287.75f₁+277f₂,and?pH=1.1775+0.001096T₁-1.02f₁-0.96f₂?.However,the established prediction models were verified between actual and predicted values by performing the additional test.The test results revealed that the nutrient solution spraying intervals had no significant effects,and ultrasonic nozzle atomization frequencies and nutrient solution spraying times had significant effects on the EC and pH values of the atomized YNS.The ultrasonic nozzle frequencies had more significant effects on the EC and pH values than the nutrient solution spraying times.The f₃ ultrasonic nozzle had significantly affected the EC and pH values of the YNS compared to the f₁ and f₂ atomization frequency.The order of the aeroponic factors affecting the EC and pH values of the atomized YNS was f₃ frequency>f₂ frequency>f₁ frequency>spraying times>spraying intervals.In addition,the compared results between actual and predicted?EC and?pH of the atomized YNS disclosed that the developed prediction models were highly significant.Because when f-T₁=28 kHz-10 minute?min?and 1.7 MHz-120 min,the total relative errors between actual and predicted?EC and?pH of the atomized YNS were 8.41%,3.61%,4.7%and 3.1%,respectively.The compared results between actual and predicted values showed that the results were very close to each other.In the other experiment,the selected nozzles were air-assisted electrostatic nozzle?A1?,centrifugal atomizing nozzle?A2?,and high-frequency ultrasonic nozzle?A3?and the selected nutrient solution was SCAULVFB.Based on the experiment data,the linear regression analysis was used to establish the prediction models^*.^*?such as?EC=9.732+?0.268*A1T1?,?pH=0.03430+?0.004787*A1T1?,?DO=0.2272+?0.005682*A1T1?,?T=-0.0200-?0.01700*A1T1?and others?.The regression analysis results revealed that the nutrient solution spraying intervals had no significant effects,and aeroponic nozzles and nutrient solution spraying times had significant effects on the physicochemical properties of the atomized SCAULVFB.Besides,the aeroponic nozzles were more effective than the nutrient solution spraying times.The A3nozzle had more significantly affected the physicochemical properties of the atomized SCAULVFB compared to A1 and A2 nozzles.The order of the aeroponic factors affecting the physicochemical properties of the SCAULVFB was A3 nozzle>A2 nozzle>A1 nozzle>spraying times>spraying intervals.The compared results between actual and predicted values in physicochemical properties of the atomized SCAULVFB disclosed that the developed prediction models were very precise.Because when A-T1=A1-50 min,A2-70 min,and A3-90 min treatments,the relative errors between actual and predicted physicochemical properties of the atomized SCAULVFB were ranged from 1%to 11%.The errors between actual and predicted?EC,?pH,?DO and?T at A-T1=A1-50 min,A2-70 min and A3-90 min treatments were 4.05%,3.12%and 4.03%,5.25%,9.25%and 4.30%,4.35%,2.89%,and 10.27%,2.35%,4.00%and 9.53%,respectively.The compared results between actual and predicted values showed that the results were very close to each other.Therefore,both test results recommended that the high-frequency?1.7 MHz?ultrasonic nozzle is not suitable for designing the aeroponic system when using the YNS and SCAULVFB as aeroponic nutrient solution.The air-assisted electrostatic nozzle and centrifugal atomizing nozzle are the suitable choices for designing the aeroponic system.In addition,in both experiments,the compared results between actual and predicted physicochemical properties of the atomized YNS and SCAULVFB disclosed that the developed prediction models were precise.The developed models can be used to predict the effect of aeroponic system working parameters on the physicochemical properties of the atomized YNS and SCAULVFB.3.Effects of different droplet sizes on growth,total polyphenol content and antioxidant activity of lettuce plantThis study aimed to determine the effect of different nozzles?droplet sizes?on lettuce growth,total polyphenol content,and antioxidant activity.In this study,A1=air-assisted nozzle(D_av=23.281?m),A2=centrifugal atomizing nozzle(D_av=46.386?m),A3=ultrasonic nozzle(D_av=3.451?m)were selected as the aeroponic nozzles.The SCAULVFB was selected as a test nutrient solution,and nutrient solution spraying time and nutrient solution spraying interval was set at 20 min‘on'and 3 h‘off'.Moreover,the findings of this study and the general analysis of the data allowed us to conclude that in the aeroponic system,the nozzle droplet size should be considered an important factor.The statistical analysis results of the data at p<0.05 showed that leafy lettuce plants treated with the A2 aeroponic nozzle(D_av=45.3?m)had comparatively higher growth,total polyphenol content,and antioxidant assay of leafy lettuce compared to those treated with the A1(D_av=23.281?m)and A3(D_av=3.451?m)aeroponic nozzles.Based on the experiment results,it was concluded that the aeroponic system designed with A2 nozzle,nutrient solution spraying time,and nutrient solution spraying interval of 20 min‘on'and 3 h‘off'can be selected to cultivate the lettuce plants in aeroponic system.This combination can significantly improve the growth,total polyphenol content and antioxidant activity parameters of the leafy lettuce plants when using SCAULVFB as a nutrient recipe.Furthermore,we recommend that further studies should be conducted by using different nozzles?droplet sizes?as a nutrient supply source in aeroponic system for other cultivars.4.Effects of different nutrient solution spraying intervals on the growth,development,and nutrient uptake parameters of the lettuce plantThe presented study aims to determine the effects of different nutrient solution spraying intervals on the growth,development,and nutrient uptake parameters of the aeroponically cultivated lettuce plants.Four different nutrient solution spraying intervals?T1=30 min,T2=60 min,T3=90 min and T4=120 min“off”?were selected as test influencing factors and analyzed with four types of the aeroponic nozzles?A1=air-assisted electrostatic nozzle,A2=air-assisted nozzle,A3=centrifugal atomizing nozzle,and A4=ultrasonic nozzle?and one nutrient solution spraying time?10 min“on”?,respectively,to atomized the SCAULVFB.While,the hydroponic system was selected as test control system to compare the results.The regression analysis?p<0.05?was performed to assess the effects of test selected factors on the growth,development,and nutrient uptake parameters of the lettuce plants.The mathematical models^*were established using polynomial regression analysis to predict the aeroponic working factors'effects on the growth,development,and nutrient uptake parameters of the lettuce plants,and the predicted values were verified by actual values.^*?such as CHL=-0.001?A₁T_N²?+0.1884?A₁T_N?+15.06,SD=-0.0004?A₁T_N²?+0.0741?A₁T_N?+1.06,LA=-0.0029?A₁T_N²?+0.4881?A₁T_N?+13.32,NLP=-0.0022?A₁T_N²?+0.3561?A₁T_N?+13.46,SL=-0.0015?A₁T_N²?+0.2929?A₁T_N?+9.61,RL=-0.0034?A₁T_N²?+0.6031?A₁T_N?+26.6,N=-3E-05?A₁T_N²?+0.0049?A₁T_N?+0.1206,P=-5E-06?A₁T_N²?+0.0008?A₁T_N?+0.0256,K=-1E-05?A₁T_N²?+0.0017?A₁T_N?+0.1897 and others?.The test results revealed that the nutrient solution spraying intervals had significant effects on the growth,development,and nutrient uptake of the aeroponically cultivated lettuce plants.The lettuce plants treated with the A3 aeroponic nozzle and T1,T3,and T4“off”had comparatively higher growth,development,and nutrient uptake parameters compared to those treated with the A1,A2,and A4 aeroponic nozzles.The orders of the aeroponic factors affecting the growth,development,and nutrient uptake parameters of the lettuce plants were A4>A2>A1>A3 and T4>T1>T3.The A4 nozzle had significantly affected the growth,development,and nutrient uptake parameters of the lettuce plants.The lettuce plants treated with A4-T1,T3,and T4“off”treatments were significantly lower than those of the A1-T1,T3,T4,A2-T1,T3,T4,A3-T1,T3,and T4“off”,respectively.Thus,it was concluded that 10 min“on”time treatment and 60 min,90 min and 120 min“off”time treatments are not suitable to cultivate the lettuce plants in the aeroponic system when using A4 nozzle as nutrient supply source.Furthermore,the lettuce plants could be cultivated at 10 min nutrient solution spraying time and 60 min,90 min,and 120 min nutrient solution spraying intervals in the aeroponic system when using A1,A2,and A3 aeroponic nozzles as SCAULVFB nutrient delivery source.However,the combination of A3-T3 treatment is recommended to cultivate the lettuce plants in the aeroponic system for significantly higher growth.The compared results between hydroponic and aeroponic systems showed that most of the growth parameters of the lettuce plants were significantly higher in the lettuce plants cultivated with the aeroponic system.However,the nutrient uptake parameters of the lettuce plants cultivated in hydroponic system were significantly higher than aeroponic system.Moreover,the compared results between actual and predicted values in the growth,development,and nutrient uptake parameters of the lettuce plants disclosed that the established prediction models were highly precise.Because when the A1,A2,A3,and A4 nozzles were used to atomized the nutrient solution at 10 min“on”and 60 min“off”,the relative errors between actual and predicted values in the growth,development,and nutrient uptake parameters of the lettuce plants were ranged between 1%-20%,respectively.The observed errors between actual values and predicted values of CHL treated with A1,A2,A3,and A4 aeroponic nozzles and 10 min“on”and 60 min“off”were6.97%,7.72%,9.00%,and 3.48%;Those of SD were 12.63%,5.30%,11.74%,and 00.67%;Those of LA were 14.34%,16.57%,11.21%,and 5.76%;Those of NLP were 13.05%,09.72%,15.56%,and 0.031%;Those of SL were 17.37%,15.80%,14.07%,and 01.44%;Those of RL were 8.49%,9.93%,6.02%,and 2.36%;Those of N uptake were 18.57%,6.39%,14.62%,and 1.67%;Those of P uptake were 17.38%,12.68%,20.79%,and 05.31%;and Those of K uptake were 9.10%,2.25%,14.67%,and 3.14%,respectively.The compared results between actual and predicted values disclosed that the developed prediction models were precise enough.The developed models can be used to predict the effects of aeroponic system working parameters on the growth,development,and nutrient uptake parameters of the lettuce plants.Besides,the engineers,plant scientists,and people interested in aeroponic cultivation should find the developed models useful for practical application of the system.In general,based on the design of series aeroponic systems,this thesis systematically studied the effects of the main working parameters of aeroponic cultivation on a global scale.The research in this thesis shows that the working parameters of the aeroponic cultivation have a significant influence on the growth,development,and quality of the cultivated plants.The main parameters affecting the cultivated plants include nozzle droplet size,nutrient solution spraying time,nutrient solution spraying interval,and nutrient solution temperature.Compared with other cultivation methods,aeroponic cultivation has the advantages of rapid crop growth,extreme water-saving,and fertilizer saving,but the premise is to choose suitable nozzles?droplet sizes?,spraying time,spraying interval and nutrient solution temperature.