Abstract
Redox potential (Eh) of soil has been measured to know the redox state in paddy soil. However, it was difficult to get reliable data because the Eh values in the field fluctuated largely. Although the measurement method had been examined to improve the problem since the 1950’s, it still remained to be analyzed. To improve the problem, we used the cyclic voltammetry (CV) to examine the reaction of the platinum electrode. The results obtained were as follows. The causes that fluctuated the data consisted of two factors. One was the chemical reactions of platinum
electrode with the surrounding materials. The other was associated with the property of the soil. The platinum electrode induced reaction with oxygen in the oxygenated medium and made oxide layer in the surface of the electrode. This layer disturbed to make the Eh stable. Polishing the sensor could remove the layer. In the reductive state, the sensor adsorbed some materials in the reductive state around its surface. This also decreased the stabilizing time. In addition, the diffusivity of ions in the soil was too small because of the large surface area and electro double-layer of soil solid. These factors decreased the moving speed of electron or ion
transport and non-equilibrium condition was formed in the soil.
