The actual state of damage to paddy rice in paddy fields established from sediment dredged from rivers

In order to solve the problems with paddies, in the case of soil dredging for the establishment of strong gley paddy fields from rivers we examined the growth and yield of paddies as well as problems occurring after their construction. The results are summarized as follows: (1) The total sulfur content of the sediment was 4-25 g kg(-1), and, when the soil was oxidized with hydrogen peroxide, its pH(H2O2) was 3. We concluded that the sediment was an acid sulfate soil because the Ex-MgO content was higher than the Ex-CaO content. (2) In the stockpile, the clayey sediment accumulated on the surface horizon whereas the sandy sediment accumulated on the subsurface horizon. After sediment accumulation over 6-8 months, oxidation of acid sulfate materials contained in the clayey sediment occurred only in the surface horizon. (3) One year after paddy field construction, the sandy paddy soil showed a lower pH(H2O) than both the clayey and loamy paddy soils,although the pH(H2O) of the sandy paddy soil increased for a few years after the construction of the paddy fields. The pH of the loamy paddy soil, on the other hand, declined. (4) In the sandy paddy fields, salt damage in the first crops was frequently found after land construction, whereas in the loamy paddy fields, salt damage was hardly found in the first crops but very poor yields occurred from the second and third crops. (5) There were differences between plant heights and the number of tillers on the border at soil pH(H2O) 4.5; plants were short, and the number of tillers was low in fields below pH(H2O) 4.5. The yield, which showed the same tendency as above, was less than 1500 kg ha(-1) in the field with pH(H2O) 4.5. (6) In paddies with sandy soil, salt damage was limited to the first crops, although the growth of rice plants in the paddy was restrained because the high solid ratio interrupted the growth of rice plants in the paddy