Studies on Formation of Paddy Soils (Part 3) : Distribution of Free Oxides in Dry Paddy Soil Profiles Developed in Flood Materials, Deposited on Old Matured Profile

Abstract

In this paper, the distributions of free oxides in two dry paddy soil profiles are reported. Both soils have developed in flood materials, deposited about eighty years ago, and have become old matured paddy soils. Their parent materials are cherty and rich in gravel. The structures develop well. The levels of ground water are low, and gley horizons are not found within 1 m below the soil surface. The profile-characteristics of these soils are given in Table 1 and mechanical compositions, in Table 2. Free oxides were determined by the Mg-reduction method and the results are given in Table 3 and Fig. 1. Total oxides were determined by the HF-treatment and the results are given in Table 4. The relationships between amounts of total oxides and those of free oxides were calculated from Table 3 and 4,and the results are given in Table 5. From the above results and observations of profiles, the following could be concluded. a) Both the third Horizon in Soil A and the fourth in Soil B are the old furrow slices. b) In Soil A, the new profile develops on the old profile without erasing the characteristics of the old one. c) In Soil B, free iron oxides, leached out of present furrow slice, accumulate mainly in the second horizon, but manganic oxides, in the third (old furrow slice) and the lower ones. Therefore the old profile has been altered in some degree.