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 combined horizontal penetrometer was designed for the on-the-go and simultaneous measurement of soil water content and mechanical resistance. The maximum sampling rate for both sensors was 10 Hz and the maximum operating depth was 20 cm. For the water-content sensor, its measurement principle depends on the electric field of the fringe-capacitance. In order to evaluate the applicability of this combined penetrometer, four experiments in the field were carried out. These experiments included: (1) soil water content profiles test; (2) soil compaction measurement test; (3) effect of the operating velocity on the water content and resistant force measurement; (4) effect of operating depth on the force measurement. The experimental results show that the combined horizontal penetrometer is a practical tool since it can provide more useful information of soil physical properties.

Three types of optical sensors at wavelength ranging from visible to NIR, were used in laboratory environment for determining soil moisture content. Some index was defined to reduce measurement error caused by scatter. Two different sands and clay were tested from air dry to saturated conditions. The test results demonstrated that all tested sensors were very sensitive to soil texture and particle-size distributions. Because the wavelength from visible to NIR varies within the sizes of sand and clay, soil should not be viewed as a material with homogeneous property under optical measurement methods.

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