Main Factors Affecting FDR Soil Moisture Sensor And Structure Optimization

Soil is the essential means in agriculture production, and its water content affects wateruptake of crop, as well as nutrient exchange. It is necessary to accurately measure soil watercontent in real-time in the arid and semi-arid areas. There are many soil water contentdetecting methods. Because of low cost, rapid measurement, and easy operation, thefrequency domain reflection has a wide range of applications in the market. Most of theexisting soil water content detectors, based on frequency domain reflection, do not take soilbulk density into influence of the dielectric properties of soil. Others use composite sensor tomeasure soil bulk density, but its operation is more complicated. It is necessary to take soilbulk density as an influence factor of the soil dielectric property and to design a simpleconstruction sensor to measure soil water content and bulk density.Summarized the theory of soil dielectric property, the relationship among measurementsof four pin type FDR soil water content sensor, temperature, soil bulk density and soil watercontent was studied. The regression equation with the four factors was fitted. The tube sticktype soil water content probe which can measure soil bulk density was designed. The probe’smeasurement was analyzed on different frequencies, temperatures, soil bulk densities and soilwater contents. The mathematical models under different frequencies were built and itsaccuracy was verified. The main tasks and conclusions as follows:(1) soil temperature and bulk density have a significant effect on the four pin type FDRsoil water content sensor’s measurements, which proves soil dielectric property affected bysoil temperature and bulk density. the relationship of four factors-the four-pin FDR sensor’soutput current, soil water content, temperature, and bulk density-can be expressed byquadratic, and the model coefficient of determination was0.9302. The absolute error betweenthe forecast moisture content and actual moisture content is in the range of-2.64%to2.81%.The average absolute error is1.22%.(2) A tube stick type soil water content probe was designed for measuring soil bulkdensity. The probe can take soil out by soil’s adhesion, and soil bulk density is calculated bymeasuring the quality. (3) The soil water content experiment using tube stick type FDR probe was made underlaboratory conditions. The frequency, temperature and soil bulk density was found to affectthe soil dielectric constant. The mathematical models about soil water content, probe voltageratio, temperature and soil bulk density were built in separate50,100and150MHz frequencysignal source. The result of analysis mathematical models is that the150MHz signal sourcemodel is superior, and the coefficient of determination is0.8286. The determinationcoefficient between calculation soil quality water content and actual soil quality water contentis0.8649, and the absolute error is-6.46to5.79%. The average error is1.818%.