Research On Environmental Control Technology For Tomato Vegetative Growth Stage Based On Stem Diameter Growth Rate

Aiming at the difficulty in setting greenhouse environmental parameters of tomato vegetative growth stage accurately, a model predicting the growth rate of tomato stem diameter is established based on experimental analysis, and an environmental control strategy of tomato vegetative growth stage based on stem diameter growth rate is put forward. Using STM32F103ZET6 single chip microcomputer as the core controller and combined with the fuzzy PID control algorithm, the software and hardware design of greenhouse environment controller based on light and tomato growth information was completed. The experimental results show that the greenhouse environment controller can not only make the tomato in the best growth environment, but also make full use of natural light to achieve the purpose of energy conservation. Specific research works are as follows:(1)The experiment of stem diameter growth response. Changes in stem diameter of crops caused by changes in the growth of crops can directly reflect the physiological status of crops and effects of environmental factors on crops. The method of monitoring stem diameter growth is relatively convenient and harmless and can be used to measure and record the data of crop continuously. In this paper, for the response of stem diameter growth, the light and temperature experiments are carried out respectively. Light experiment is divided into three groups, namely, no treatment, a layer of shading and two layers of shading. The temperature experiment is divided into four groups, namely, 20 degrees, 23 degrees, 26 degrees and 29 degrees.(2)Establishment of the model of tomato stem diameter growth rate. The stem diameter growth rate is an important parameter describing the growth status of tomato plant during its vegetative growth stage. In order to improve the predictive ability on tomato growth, an innovative stem diameter growth rate model based on tomato’s physiological responsiveness to major environmental factors was developed. By analyzing the dynamics of tomato stem diameter, diurnal variation rate of stem diameter and hourly variation rate of stem diameter, it was found that the stem diameter measured at 3:00 am was the representative value as the daily basis of tomato stem diameter. Based on of the responses of stem diameter growth rate to light and temperature, a linear regression relationship was applied to establish the stem diameter growth rate prediction model for tomato’s vegetative growth stage, and which was further validated by experimental data.(3)Research on control strategy of greenhouse environment. Thorough analyzing the optimum temperature value of maximum photosynthetic efficiency under a certain light intensity and the response of stem diameter growth rate to physiological responsiveness, combining the decision-making technique based on different time scales, a greenhouse environment control strategy based on tomato stem diameter growth rate is put forward. Calculate the difference between actual growth rate and predicted growth rate of stem diameter, then obtain the ?PR; Based on the weather forecast information, the difference method is used to estimate the ’iPR per day; According to the current climate conditions, adjust the climate parameters to meet the target PR, and thus calculate the current RTE and RLE, and finally obtain the greenhouse environment parameter settings. The control strategy solves the difficulty in determining target value of environmental parameters, reduces energy consumption and the probability of crop emergence spindling.(4)Design of greenhouse environment controller. In order to improve the control of greenhouse environment in the period of tomato vegetative growth, a greenhouse environment controller based on stem diameter growth rate is designed. In accordance with the forecasting model and greenhouse environment control strategy, the controller takes STM32F103ZET6 single chip microcomputer as the central processing unit, and combines the advantages of the fuzzy PID control algorithm. The hardware structure and main functions of the controller are introduced, and the design of hardware and software is completed. The experimental results show that the controller can achieve good control on greenhouse environment system with large time delay, strong coupling and nonlinearity characteristics and has the advantages of saving energy and reducing economic benefits.