In order to evaluate influence of soil conductivity on capacitive soil moisture sensor and applicability of sensor to variation range of agricultural soil

a series of soil equivalent dielectric solutions whose soil equivalent water content is 40.6 % and conductivity is at the range of 0

1.91 dS/m is prepared

and experiments of variability conductance on seven kinds of sensors whose excitation signal frequency of 40

50

60

70

80

90 and100 MHz are performed by using the prepared equivalent dielectric solutions

and then four kinds of soil samples whose moisture content is 40.6% and soil conductivity o

f 0

0.31

0.46 and 0.61 dS/m respectively are prepared to verify the results tested in equivalent dielectric solutions.Test results show that 1) test results in soil samples are basically in accordance with that in the equivalent dielectric solutions

so it can employ equivalent dielectric solutions to assess variability for conductivity of sensor; 2) variation rate for conductivity of sensor has an approximately linear increase with rising of conductivity of the tested medium

and the higher the frequency of excitation signal of sensor is the smaller variation rate for conductivity of sensor is in the tested medium of same conductivity; 3) maximum variation rate for conductivity of sensor is 9.2 %

when its excitation signal frequency is not less than 80 MHz at the range of 0.239

0.650 dS/m

which is the basic conductivity variation range of agricultural soil

which can meet the requirements of engineering application.