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'Measuring mm/d water flux densities with an improved penta-needle heat-pulse probe (PHPP)'
Pawel Szafruga (pszafruga@yahoo.com), Utah State University; Kashifa Rumana (kashifarumana@aggiemail.usu.edu), Utah State University; Shmulik Friedman (vwsfried@volcani.agri.gov.il), Volcani Center, Agricultural Research Organization, Israel; Scott Jones (scott.jones@usu.edu), Utah State University

Growing populations have led to increased concern about water availability and efficient agricultural practices. The necessity for a system to instantly and accurately measure soil water and solute transport is greater than ever. However, even though advancements in instrumentation have improved measurement capabilities, there is still a lack of an accurate, in-situ method to measure soil water flux at a resolution sufficient for capturing naturally occurring processes. These processes occur at rates down to around 1 mm/d and include deep percolation, evaporation and redistribution. Evolving work over the last few decades has shown that the heat-pulse (HP) method is capable of measuring in-situ water flux in soil, and has shown the capability to measure water flux densities as low as 1 cm/d. Recently, a penta-needle heat-pulse probe (PHPP) has been developed which is based on the HP method and allows for water flux measurements in a plane normal to the heater needles. Further, the PHPP is capable of internally calculating thermal properties and heat velocities, allowing for near instantaneous soil water flux calculations. By combining recent improvements to the PHPP mathematical algorithms and several programming and design modifications, it may be possible to improve the resolution of water flux density determination to 1 mm/d. Presented is a background of the methods and theories, as well as preliminary results.