Analysis To Effects Of Main Factors On Dielectric Properties Of Soils

The soil moisture is an important part of the natural soil. It not only affects the physicalproperties of soil, but also restricts the nutrients dissolution, the transform and activities ofmicrobial and is an important index of soil fertility. Therefore, the determination of soilmoisture is of great significance to guide healthy crops growth. A large number of studieshave shown that the dielectric properties of materials are mainly determined by theircomposition, measured frequency, the temperature of the soil, bulk density, salinity, soilvarieties and factors on the different types of soil dielectric properties lack syetem research.The dielectric properties of soil were studied in order to provide a basic data for highprescision soil composition testing instrument.The effect of frequency (10M~4500MHz), temperature (5~50℃), soil moisture, bulkdensity and the influence of salinity on dielectric properties of black, red and yellow soil werestudied. The internal mechanisms of these factors were studied and the relationships betweensoil components information and dielectric properties of soil were researched. Theconclusions are as follows:(1) The dielectric constants of soil were decreased with increasing frequency with10M~4500MHz, while the dielectric loss factors were changed from increase to decrease,then to increase. Both dielectric constant and loss factor were increased with increasingmoisture content and temperature over the detected range. The dielectric constant anddielectric loss factor had significant changes in low frequency than high frequency.(2) Dielectric constant and dielectric loss factor were increased with the rising oftemperature, especially under the high moisture content, the temperature had significantlyeffects on dielectric constant In the10M~4500MHz frequency range, the dielectric loss factorof soil, included black, yellow and red clay, had different levels of dielectric relaxationphenomenon. The clay had the lower dielectric loss factor than others, within10to4500MHz,dielectric relaxation phenomenon was obvious. The penetration depth was decreased withincreasing frequency, moisture content, and temperature and bulk density. The reasonablefrequency for detecting moisture content of soil based on dielectric properties were over therange from50to100MHz. In the100MHz, the relationships between moisture content and actual moisture content prediction model, R~2=0.9725.(3) Dielectric properties of soil, black, yellow and red clay, were increased withincreasing bulk density. When the frequency was above500MHz, the dielectric loss factor ofdifferent bulk density for different soil tended to be a constant value. When the frequency wasless than1500MHz, the penetration depth of different kinds of soil had linear relationshipswith frequency in log-log plot. The penetration depth of soil was decreased with increasingbulk density and moisture content.(4) The dielectric constant and loss factor of saline soil were increased with increasingmoisture content and salinity. In high salt content conditions, the dielectric loss factor wassignificantly increased than before, showed a strong linear correlation in plot-linear plot.However, when the frequency increased and tended to be stable scale, the dielectric propertiesshowed the opposite rule. Without the knowledge of soil varieties, the coefficient ofdetermination value and predict value was0.9294.This study not only contributed to an understanding of the main factors on the influenceof different types of soil properties, but also developed a comprehensive measurement modelfor soil moisture sensor with temperature and volume density and salinity compensationfunctions.