Study On Nutrient Solution Control System Based On Characteristic Leaf Length

At present,the nutrient control system of greenhouse developed in China can be divided into two categories:A-B box open-loop nutrient control system and closed-loop control system.Both two systems realize automatic control of greenhouse.However,the inadequacy is that it can not be irrigated with nutrient solution according to the demand of the crop,which leads to the low utilization rate of nutrients,and does not meet the requirements of high efficiency,high yield and quality of modern agriculture.Therefore,there is an urgent need to strengthen the research on the characterization methods of crop nutrient status,and to explore the law of crop nutrient demand according to the indicators of characterization.Finally a nutrient solution management system that can manage nutrient solution based on the law of crop nutrient demand.In this paper,characteristic leaf length was selected to represent the nutrient supply of tomato,and a strategy of nutrient solution management in Greenhouse based on characteristic leaf length was proposed.Finally,a nutrient solution management system based on characteristic leaf length was developed.In this paper,different concentrations of nutrient solution were designed to irrigate greenhouse tomatoes.The growth status of leaves at different nodes was determined,and then the characteristic leaf position was determined.By analyzing the relationship between characteristic leaf length and nutrient solution concentration,a nutrient solution management strategy based on characteristic leaf length was established.A nutrient solution management system based on the characteristic leaf length was developed through programming and hardware assembly.The contents of research are as follows:(1)Selection of characteristic leaf lengthIn this paper,the response of leaf length,plant height and fruit diameter to nutrient solution concentration during the whole growth and development period of tomato under different nutrient solution concentrations was studying.The following conclusions were drawn:at the seedling stage,the relationship between characteristic leaf position and the total leaf number was as follows:y(28)1.12x-5.33(7)7?x?(16)(19)(8).At flowering and fruiting stage,the relationship between characteristic leaf position and the total leaf number was as follows:y(28)1.13x-5.61(7)15?x?(17)(22)(8).(2)Prediction model of blade lengthIn order to explore the relationship between nutrient solution concentration and the tomato leaves length of greenhouse,the experiment of different nutrient solution concentration on greenhouse tomato leaf length was designed(Experiment 1).The effects of different nutrient solution concentration on the average growth rate and maximum leaf length of greenhouse tomato leaves were quantified.A prediction model of greenhouse tomato leaf length was established,and the model was validated with experimental data independent of the modeling data.The purpose of this study is to quantify the effect of different nutrient solution concentrations on the leaf length of tomatoes in greenhouse,and to establish a prediction model of actual leaf length under different nutrient solution concentration based on the results of quantification,which provides a theoretical basis for the establishment of nutrient solution regulation model based on leaf length.The results showed that the concentration of nutrient solution significantly affected the average growth rate and maximum leaf length of greenhouse tomato leaves.The R~2 of the model was 0.30 and RMSE was 0.22 cm/°C between the predicted results of the model for the average growth rate of greenhouse tomato leaves and the 1:1 line.The R~2 of the model was 0.77 and RMSE was 7.78 cm between the predicted maximum leaf length of the greenhouse tomato and the 1:1 line.The R~2 of the model was 0.71 and RMSE was 9.71 cm between the predicted actual leaf length of the greenhouse tomato and the 1:1 line.This simulates the growth of tomato leaves in greenhouse and improves the reliability and practicability of the greenhouse nutrient supply decision model in China.(3)Design of hardware and software for nutrient solution control systemIn order to improve the effect of greenhouse tomato nutrient solution irrigation,a set of greenhouse tomato nutrient solution control system was designed based on the decision-making model of greenhouse tomato leaf length nutrient solution supply,which realized the automatic control of nutrient solution concentration according to the characteristic leaf length of greenhouse tomato.The hardware structure and system composition of the control system are introduced,including software design,PLC control design,liquid level monitoring design,interface design and formula design.Detailed function description and program flow chart are given.The control system proposed in this paper uses S7-200PLC as the core controller,using liquid level transmitter,temperature transmitter and clock control to realize fine-tuning irrigation of tomato nutrient solution in greenhouse.This system improves the utilization efficiency of nutrient solution and reduces the economic cost.It saves the irrigation of nutrient solution on the basis of improving the economic benefits of tomato in greenhouse.