A small multi-needle probe for measuring soil thermal properties, water content and electrical conductivity

Ready access to reliable low cost instrumentation for use in laboratory and field experimentation remains a priority for many working in the soil and environmental sciences area. In this paper we provide an overview of the multi-needle heat-pulse probe which can now provide measurements of soil temperature, soil thermal diffusivity, volumetric heat capacity, thermal conductivity, volumetric water content, and bulk soil electrical conductivity, all at the same position and time. We show that the multi-needle probe can provide high quality measurements, in some cases as good as or better than those obtained using other current methodology. As an example, multi-needle probes have been shown to yield measurements of volumetric water content with a root mean square error of 0.01 m(3) m(-3). Because of its small size the multi-needle probe should prove particularly useful for measurements near the soil surface, near to plant roots, and in other situations requiring fine spatial resolution in measurements. These probes can also be easily automated for unattended use to facilitate data collection as a function of time and space. We also highlight issues that need further analysis and research in helping guide further development of more robust multi-needle probe designs, especially for field applications. (C) 2001 Elsevier Science B.V. All rights reserved.