Profile Moisture Detection System For Multiple Soil Environments

China is a great agricultural country,and 2/3 of the country’s total water consumption is used for irrigation every year.However,domestic water resources are critical shortage,and the per capita share is only about 25% of the world average.In order to alleviate this contradiction,modern agriculture must be developed toward precision agriculture.The implementation of precision agriculture is an important way to achieve water-saving irrigation and sustainable agricultural development.The detection and control of soil water content is a key technique for precision agriculture.However,the existing soil moisture sensors need tedious calibration for different soils.To solve this problem,the structural parameters and performance indexes of the designed sensor were studied theoretically,and the optimal design of the sensor was realized.Secondly,the relationship between soil sand content and capacitance-water model was studied,a calibration-free moisture detection method for multiple soils was proposed.Finally,the One NET cloud platform was used to realize the field application of the sensor.This paper mainly completed the following four aspects of work:1.Based on the difference of dielectric properties of soil,the relationship between the equivalent capacitance of fringe electric field sensor and soil moisture was studied.We used Maxwell to simulate the performance of sensor.The effects of electrode spacing,electrode structure and the number of interdigitated electrode pairs on sensor sensitivity,signal strength and penetration depth were analyzed by finite element method,and the optimized structure of sensor was determined.2.The core circuit of the conductivity sensor was simulated by using Multisim software,which simplifies the circuit design scheme of AC source and effectively reduces the influence of polarization phenomenon on the experimental results.Based on this,the multiplex sensor plate with time-division acquisition function of capacitance and conductivity was designed,which makes the whole system compact and easy to install on site.3.Five soil samples with different sand contents were prepared based on the Kachinsky soil classification method,and the temperature compensation algorithm for different soil capacitance and conductivity was studied through temperature variation experiment.The relationship between capacitance-water model and soil sand content was further analyzed,and a calibration-free moisture detection method is proposed,which is suitable for a variety of soil environments(except pure sandy soil),with a maximum measurement error of 3.8%.4.The software and hardware design of automatic detection system were completed,and a sensor network using Lo Ra and One NET was built.The system was automatically monitored outdoors in situ in 2019.The results show that the designed sensor can well reflect the actual situation of artificial irrigation and rainfall,and it has potential application value.