A soil moisture sensor with low-cost, reliability and sufficient accuracy has been desired for many years. This paper presented an improved measurement method based on FD principle for determining soil water content. Unlike other measurement principles, a new measurable index, which is independent of the output impedance and the amplitude of the oscillator but relies on the electric impedance of the multi-pin probe, was proposed. Moreover, a model for treating the impedance of the multi-pin soil probe was also discussed and several important electric properties were approached. In order to confirm the theoretical analysis, the necessary experiments were conducted. Finally, using obtained modeling, the relationship between the proposed index and soil volumetric water content was linearly corrected.

A dual sensor combining dielectric and mechanic principles wasdeveloped. The geometric structure of this sensor has been designedaccording to the ASAE-standard for penetrometer cones, and the sensorcan provide a pair of output signals when inserted into soil. By analyzingboth signals, one can determine the correlation among cone index, soilbulk density, and moisture content. Some preliminary experiments wereperformed in a laboratory environment, and the sensor will be ready foruse in the field in the near future.

A soil moisture sensor with low-cost, reliability and sufficient accuracy has been desired for many years. This paper presented an improved sensor for determining soil water content. Unlike other measurement principles, an index, which is independent of the output impedance and the amplitude of the oscillator but relies on the impedance of the multi-pin probe, was proposed. Moreover, a model for treating the impedance of the multi-pin probe was also discussed and the necessary experiment was conducted. Finally, the relationship between the proposed index and soil volumetric water content was linearly corrected.

A polarized He-Ne laser light was used in a laboratory environment to measure soil moisture content. Depolarization of the light beam was used as an indicator of dielectric constant, which, in turn, indicated soil moisture content. Fourier analysis was used to analyze the signals. The DC component and the second harmonic of the Fourier spectrum were used to calculate the degree of depolarization. This method greatly reduced the effects of noise from various sources on the measurement of degree of depolarization. Three soil types (silt-loam, loam, and loam-sand) were tested. For all three soil types, degree of depolarization decreased with an increase of moisture content. The change was most significant for loam, followed by silt loam and loam sand.

基于电流-电压四端法的“polar-djpole array”形式，以壤土作为研究对象，对土壤含水率和土壤盐分与土壤电导率之间的相互关系进行了试验研究。结果表明，在土壤盐分和含水率2个相关因素中，土壤盐分对土壤电导率的影响较土壤含水率要大得多。