2022 Volume 12 Issue 1 Pages 66-71
Soil chemical environment (SCE) affects soil degradation and productivity, thus understanding of the temporal changes of SCE is important for obtaining higher soil productivity. Widely used indices of SCE included ion concentration, pH, and redox potential (ORP), but these cannot monitor SCE continuously. Previously, a study proved that continued potential measurement can represent temporal changes in the water quality at the sea floor. However, no report related to monitoring the SCE with continued potential measurement has been found. Therefore, this study proposes a method for evaluating soil ORP using continued potential measurement, and examine the method’s validity in representing changes in SCE due to soil reduction, bacteria activation, and soil oxidation. Laboratory experiments were conducted using soils from rice paddy fields. A brush-type carbon electrode was installed in the soil layer that then connected to a reference electrode for measurement of the soil ORP. Different soil conditions were created by mixing the paddy soil with cow manure compost or potassium sulfate. The soil ORP was automatically recorded every 15 min using a voltage meter. The ORP of paddy soil decreased temporally and stabilized at 50 days after the start of the experiment, suggesting that soil reduction occurred over those 50 days. When testing the potassium sulfate-paddy soil mixture, the soil ORP rapidly decreased during the first day after the experiment started. When testing cow manure compost-paddy soil mixture, a larger decrease in soil ORP was observed compared to that in the paddy soil alone. These findings suggest that soil reduction is promoted by adding potassium sulfate or cow manure compost. Among the soil samples tested, there was a range of soil ORPs and trends in the potential decreases. Based on the results of this study, it was found that continued potential measurement is effective in evaluating soil ORP, which represents temporal changes in SCE due to redox reactions after the addition of cow manure compost or potassium sulfate. In addition, the effects of bacteria activation are revealed during continued potential measurement of soil ORP.
