土壌中の水のポテンシャルを測る新しい測定器

抄録

A new gauge was fabricated on trial by the author for measuring hydraulic potential of soil water. The null method was applied in the design of the gauge as in that of many other gauges for the same purpose.
A new feature of the gauge exists in that the pressure equilibrium is judged by the moveinent of water in the connecting tube. A water level is prepared in the movable pot for equilibrating the potential of soil water to be measured. A part of the tube connecting the piezometer opening and the movable pot is replaced by a glass capillary, and the movement of water in the capillary is observed with a microscope. The water is mixed in advance with Indian ink at a low concentration in order to facilitate the observation of water movement. The carbon particles of ink flow when not in equilibrium, and stop movement when equilibrium is attained by adjusting the movable pot.
By this method a difference of 0.1mm of water pressure can easily be observed. The precision of the method hardly changes even for 100m long connecting tube. Sensibility is lower when ceramic cup piezometer is used, and an alternation of closing and opening of cock can maintain a high sensibility. Experiments proved that the measurement of water pressure and tension in, sand or loam is easily made within 2 or 3 minutes with an error less than 1 or 2 mmAq. This gauge cannot follow rapid pressure fluctuations, but can satisfactorily follow slowly changing pressure with a practically high accuracy.