Research On The Soil PH Online Detection Sensor And Its Performance Affected By Water Content

Soil hydrogen ion concentration(pH value)has an important impact on soil fertility and nutrients.Realizing the online detection of soil pH value and giving precise control during the growth of crops are of great significance for reducing the production cost of cultivation,increasing yield,and realizing digital agriculture.This article aims at the problem that the online detection of soil pH is affected by soil moisture,and the existing sensors cannot meet the requirements for online detection of soil pH,resulting in poor online detection accuracy.Based on the current research on pH sensors at home and abroad,through the combination of micro simulation and macro experiments,the electrochemical response process and mechanism of antimony electrode to the pH value of soil micro solution are studied.An antimony electrode pH sensor was prepared to reveal the influence of soil water content on the response characteristics of the pH sensor.The water content correction model was constructed to improve the online pH detection performance.The main research contents are as follows:(1)Theoretical analysis of the detection of soil pH by antimony electrode sensors.Through the pH electrochemical reaction process and response mechanism of antimony electrode to soil micro-solution:at 25~oC,the theoretical Nernst response of the antimony electrode is 59.2mV/pH;the electrode preparation process and detection solution environment is the main factor affecting the output potential of antimony electrode sensor.Through the multi-phase mixing properties of the soil,the law of soil water and salt diffusion and the theory of electric double layer,the increasing of soil water content increases the soil diffusion coefficient and improves the accuracy of the electrochemical response of the antimony electrode.(2)The study of molecular simulation on antimony electrodes detection performance affected by soil water content.Based on molecular dynamics theory,the diffusion behavior of hydronium ions in soil media with different water contents is simulated.The results show that the mean square displacement of hydronium ions in soil is isotropic,and the diffusion coefficient increases with the increase of soil water content.Based on the first-principles simulating of the effect of water molecules on the electrochemical response of the antimony electrode.The results show that the water molecules on different positions of the antimony surface affects the adsorption results and the top adsorption structure on the antimony surface is the most stable.During the adsorption process,the charge exchange between the oxygen atom and the antimony atom in the water molecule reduces the surface potential of antimony and promotes the electrochemical reaction of antimony electrode.(3)The preparation of antimony electrode sensor and its response characteristics to the pH value of soil micro-solution.Based on the magnetron sputtering method,an all-solid pH sensor suitable for soil micro-solution was prepared with Sb and Ag/AgCl as the sensitive electrode and reference electrode respectively.SEM and EDS analysis showed that the surface of the antimony electrode has a porous structure.The high proportion antimony element,indicating that the prepared antimony electrode film had good quality.The electrochemical response experiment of pH sensor was conducted and the response characteristics of the sensor in aqueous solution were obtained:the sensor sensitivity is 57.58mV/pH,which is near Nernst response principle,the response time is less than 15s,the drift effect is 1.59mV/h,and has a good pH response stability and ion selectivity.From the analysis of the effect of soil water content on the output characteristics of the pH sensor,with the water content increases,the output potential of the sensor decreases.Based on the binary regression analysis method,the compensation model of the effect of soil water content on the pH response of electrode was established,and compensation model is proved to be effective.(4)Construction and application test of soil pH online detection system.The online detection system of soil pH value is designed by comprehensive application of sensor and wireless transmission technology.The system includes sensor acquisition module,data processing module and human-computer interaction interface.The application test for the online detection with different types of soil substrates showed that the system has is suitable for different types of soil substrates.After the correction of water content compensation model,the absolute error of the pH value is between 0.18 and 0.51 and the the relative error is between 2.2%and 6.6%.The research results provide theoretical guidance and technical basis for realizing the online detection of pH value in modern agricultural cultivation production.