Abstract
For the purpose of nondestructive determining of soil water content near the surface of a sandy field, a surface-type neutron moisture meter with the capability of making backscatter and direct transmission measurements was introduced.
In this paper, the response on this surface-type neutron moisture meter at source positions of 0, 5, 10, 15, 20, 25, 30 cm was described by an experiment using dune sand with different water contents. To know how large the sphere of importance of a surface-type neutron moisture meter is, the influence of the presence of a paraffin mass on the count ratio was examined for the dune sand in the vertical and horizontal directions. In case of the backscatter method, the radius of the sphere of importance was obtained as the function of the volumetric water content. Furthermore, calibration curves of the surface-type neutron moisture meter for the source depths of 0, 5, 10, 15cm were determined for a dune sand in a calibration vessel. Therefore, the utility of the calibration curves to measure the soil water content in a sandy field was discussed by the experiment with a relatively higher water content in a lysimeter during drainage and by core sampling with a relatively lower water content in an actual sandy field. As a result, it was recognized that the calibration curves for source depths of 5 and 10 cm could be practically used to monitor the soil water content near the surface in an actual sandy field within the measuring error of 1% by volume.
