Determination of soil water content in situ is complicated due to variations in dielectric constant of porous media. Time domain reflectometry (TDR) may meet the need for measurement of soil moisture with high accuracy. However, TDR-type instruments are expensive. A theory, which is called standing-wave ratio (SWR) of transmission line, is proposed in this paper. This theory has been proven a valuable tool for measuring soil water content. A method for calculating the characteristic impedance of a four-wire probe was developed. Furthermore, a prototype of a SWR-type sensor equipped with a new soil probe was designed.The measurement error was found to be within

土壤介电常数是影响土壤含水率快速、准确和可靠测量的关键参数。通过检测土壤介电常数换算出土壤含水率的测量方法已成功地应用在基于TDR原理的现代先进测量仪器中。文中依据传输线理论探讨了基于驻波比原理的土壤介电常数测量方法，解决多针探头特征阻抗的计算，实验结果证实了理论分析的正确。

现代农业正朝着知识农业的方向发展。为此，在分析精细农业的含义及其技术思想的基础上，结合新疆绿洲农业现状，提出了适合新疆情况的精细农业发展策略，对推动新疆由传统农业向现代化农业转化具有一定意义。

Based on the theory of the impedance-transform of transmission line, a mathematical model for calculating the impedance of a soil probe with a multi-pin structure was developed. It is found that the impedance of the multi-pin probe may be turned into an inductive-reactance from a capacitive-reactance and vice versa as measurement conditions change. Moreover, the formula for the impedance of a soil probe has a series of periodical discontinuous dots. Three necessary experiments to verify this model were conducted in a laboratory environment. By changing the measurement frequency (50-200 MHz), the length of the pin (5-15cm) and the number of pins (2-5), some electric properties of the multi-pin probe were confirmed. As an application of the model, a prototype was designed and it achieved a measurement accuracy of volumetric soil water content within

A combined penetrometer is an appropriate tool to measure the soil cone resistance and the water-content profile. As arelatively new technique, acombined capacitance-penetrometer for the simultaneous measurement of cone index and soil water content was developed at the Department of Agricultural Engineering of Bonn University in 2002. The objective of this study was the evaluation of the effectiveness and applicability of the innovated penetrometer with a focus on three aspects: (1) A capacitance sensor with two electrode configurations was calibrated for silt loam, sandy loam, and sand. The calibration results show that both electrode configurations have sufficient water-content sensitivity, but soil-specific calibrations seem necessary.(2) Under laboratory conditions, the dynamic resolution and response of the capacitance-penetrometer were validated, and its radius of influence was determined.(3) The field measurement results demonstrate that this measurement technique can be used to improve the interpretation quality of soil cone index data.