中性子土壌水分計の実用化について

畑地を対象にした中性子土壌水分計に関する研究 (II)

抄録

As mentioned in the preceding paper, the sphere of measurement of neutron soil-moisture meter increases with decreace in soil-moisture. Consequently, error in measurement results when a neutron soil-moisture meter is used foil-calculation of consumptive soil moisture.
Therefore, in this paper, the authors investigated the possibility of varying the sphere of measurement.
In order to enlarge the sphere of measurement of the surface probe, a part of the probe was laid under the ground. The relation between buried depth and increased counts was approximately linear and the effect of increasing was about 30-40%(Table 2).
On the other hand, in order to have a smaller sphere, iron plates were laid under the probe. The effect of decreasing was about 20-30%.
With regard to the depth probe, a new probe in which Cd was fixed was prepared to shield thermal neutron flux. By varying the width of the slit of the Cd shield, which was fixed around the counter, it was possible to change the sphere of measurement about 50%(Table 4).
Consequently, it was proved that the optimum sphere to be used can be chosen within these limits irrespective of soil moisture.