抄録
A new method that can measure dissolved oxygen (DO) in soil solution and redox potential (Eh) and others in several constant depths was developed. This method was used at two paddy fields, with different organic content, under farming conditions over three years. Findings are listed as follows.
① The installation was made up of a simple box (50 cm X 50 cm X 60 cm) and other instruments. Filters for sampling soil solutions and several electrodes of redox potential were set horizontally at the observation box (open lysimeter).
② Concentrations of DO in inundation were 5-8 mg/L during the ponding irrigation period. After translation of rice plants, DO in soil solution of plow layer(at 3-4 depths) became about 2 mg/L during the irrigation period. DO in soil solution increased to 5-8 mg/L during the nonirrigation period.
③ The value of Eh in plow layer decreased gradually after inundation and became a reduction layer (about —150 mV) until mid-summer drainage. If the period of mid-summer drainage did not received rain for seven days, the plow layer became oxidation layer. But the higher Eh values in the plow layer would return to similar low Eh before mid-summer drainage when inundation continued over two weeks. After the ponding water was released the values of Eh gradually increased and became the oxidation layer (over 400 mV). As the above results show, the new method clarifies that DO and Eh values of plow layer at constant depths show seasonal fluctuation.
