For the demand to monitor soil water dynamics at fi eld scale, this study presents a solar-powered wireless cell that containes a water content sensor with a communication module and a data-logger. The electronical components and the operation mode were designed to reduce the energy demand and to attain a continuous operation even under the canopy of fi eld crop. To evaluate its feasibility in the fi eld, three cells were independently installed in a bare plot, a maize plot and a sugar beet

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... for a period of two months. Abstract Landtechnik 65 (2010), no. 6, pp. 442-445, 5 fi gures, 1 table, 7 references ■ Soil water content plays an important role in governing crop growth and yield. To monitor soil water content dynamically in the root zone a sensor technique, which has high accuracy and reliability , rapid response, low energy consumption and cost, is desired [1; 2]. Earlier techniques for this purpose were a plaster sensor and tensiometer, but their response was unsatisfactory and there was hysteresis error between wetting and drying [3]. Since Topp et al. [4] presented a three-order polynomial to approximate the relationship between VSWC (volumetric soil water content) and relative diel-ectric constant (ε r) of moist soil, various dielectric sensors, based on TDR (time domain refl ectometry) and FD (frequency domain) principles , have been developed and have become commercially available [5]. TDR sensors only take a number of seconds to complete a water content measurement [6]. A more rapid response can be achieved with a FD sensor, which only needs a fraction of a second [7]. Thus, both sensors can meet the requirement of dynamic measurement. However, there are still some technical limitations for these dielectric sensors to be a node of wireless network. One of the main limitations is to supply a long-term power to the sensors that are remotely and stand-alone located. Another demand is to wirelessly transfer the data with other sensors, data-loggers or routers across a certain distance. In this study, a solar-powered wireless cell for the dynamic measurements of soil water content in the root zone was designed and then a fi eld evaluation was conducted under three canopy conditions.