Regarding mineral pollution of the river Watarase, studies were made on the properties of its irrigating quality and also on its harmful effects on the growth and yield of paddy rice plant. The results obtained were as follows : - 1. Surface water of the river Watarase was clear and neutral in its reaction and did not contain copper in fine weather, consequently it was suitable for irrigation. But in rainy weather it became very muddy and floated much sand and mud which contained a considerable amount of copper. This amount of copper, taken into the paday field, caused the crops to suffer from the injurious effect of this metal due to the unfavourable conditions occurred in both chemically and physically. If these floating solid matters were removed from the muddy water, the harmful effect would be expected to be got rid of. 2. Ground water from the river Watarase was good in its chemical composition, but had rather lower temperature even in midsummer compared to that of the surface water. Therefore the water needed to be warmed when it was used for irrigation. 3. Harmful effects on the growth and yield of paddy rice plant were due to not only the excess of Cu ion derived from the floating solid matter in muddy water, but also the unfavourable physical conditions of soils. 4. From the point of view of utilisation for irrigation the water was required, first of all, to be free from the floating solid matters, which caused the harmful effects on the rice plant. For the protecting the field from the shortage of irrigating water, the use of ground water was taken. into consideration.

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In Japan, as a whole, peat lands are mostly used as paddy field for rice culture. It is also the same in Hokkaido so long as the climatic conditions permit the growth of rice plant as in the case of Ishikari district. The yield of rice from that type of land is high if the weather is favourable, while it is very low in the cold year compared with the yield of ordinary mineral soils. In order to make clear the reason, writers undertook to make a comparison of the metabolism of rice plants grown in peat soil with those grown in mineral soils, as well as to study the edaphological characteristics of peat soil. The following conclusions were reached : 1) After flowering poriod when the demand of rice plant for nitrogen becomes low, the decomposition of peat occurs and liberates soluble nitrogen. In the case of a cold year, that period is delayed until later causing a disturbance in the normal metabolism of rice plant as occurs also in case of delayed top-dressing of ammonia. 2) Peat soils in Ishikari district are low in potassium content, and, moreover, that content decreases markedly at the flowering stage of rice plant. So, rice plant becomes deficient in potassium just when the plant needs it remarkablly. 3) The volume weight of peat soil is very low. Especially it becomes low in paddy field condition, because methan-gas is produced as the result of decomposition of peat. So, the rice plants contact comparatively small amounts of nutrients in the soil surrounding their root.

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The author studied absorption spectra of natural and artificial hnmic acid solutions. The results were summarized as follws : l. The intensity of light absorption of humic acid dissolved in dilute alkaline solution decreased gradually with the lapse of time at all waves, especially remarkably at long waves. But in ultra-violet region, the absorption intensity tended to increase again after about 50 days. In the case of soil humic acids, the decrease of light absorption became greater with the lowering of humification. Artificial humic acids were very unstable compared with natural soil humic acids (Table l). 2. The absorption curves of the soil humic acids hardly changed their shapes after the acids was reprecipitated 5 to 7 times, but the curves of artificial humic acids showed an inclination of getting steep shape after the reprecipitation. This inclination was probably due to the partial decomposition or denaturation of the acids (Table 2). 3. No visible bands were found in the absorption spectra of humic acids in the visible region except in those from podsol and diluvial soil (Fig. 1 and 2). The humic acids from these soils showed absorption bands clearly at about 620 mμ and somewhat indistinctly at about 570 and 470mμ. 4. Absorption curves of humic acids were very similar in their shapes at the waves, from 200 to 2,OOOmμ having a lowest part at about 1,100mμ, and turning upward from this wavelength (Fig. 3).

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In this paper, the sedimentation volume and the colloidal state of water-logged paddy soils were investigated. It was welltimed to measure the sedimentation volume 2 hours (5 hours in special case) after shakig the plugged glass tube. The coagulation degree of water-logged paddy soils were measured by the apparatus showed in Fig. 1. Fe^<II> ions, formed in the reductive layer, decreased the negative charge of soil colloids as the bivalent positive ions. So in the cases of normal paddy soils, which contained a large amount of free iron, the soil colloids in reductive layer were in the jelly state, and soils were brought to be coagulated solidly. On the other hand, in the cases of aged paddy soils, which contained a small amount of free iron, the soil colloids were in the sol state, and the soils were not to be coagulated as the former due to the action of H_2S.

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The efficiency of soil conditioners for the formation of water stable aggregate with various conditions was investigated. The results were as follows : 1) The water stable aggregates of soils treated with three synthetic soil conditioners, such as Krilium, carboxy methyl cellulose and A-22,were estimated by modified YODER'S method. And we observed that the soil contained many small particle size had the excellent water stable aggregate forming efficiency. And so it was seemed that the particle size of the soil was an important factor for the water stable aggregate formation by the soil conditioners. (Table 1,2) 2) The water stable aggregates of the soils treated with 6% H_20_2 were estimated and their values were compared with those of original soils. Consequently, it was seemed that the humus in soils did not affect the water stable aggregate forming efficiency with the soil conditioners. (Table 2) 3) To pursue further the significance of the particle size of soils for the formation of water stable aggregate, coarse sand, fine sand, silt and clay were separated, and the each particle was treated with three kinds of methyl cellulose. The absolute viscosities of 1% water solution of them were 1,500,400 and 100 centi pois, respectively. And it was seemed that clay had the most excellent water stable aggregate forming efficiency, the silt was the next, the coarse sand and the fine sand not form aggregates. (Table 3)

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It is the purpose of this paper to study the effects of iron sulfides which had been formed in polder soils under an anaerobic condition on the soil forming processes of polder soils of Kojima Bay. The content of FeS_2 in the non-leached halogenetic polder soils is over 0.5% as SO_3 in most of horizons. Iron sulfides in the leached halogenetic polder soils decrease greatly in the upper horizons, ranging from 0.1 to 0.2%, but those of G horizons are 0.5% or more. It is found that iron sulfides are rapidly oxidized in an aerobic condition and their products are easily leached out and the reaction of soils becomes acid as a result of this change. On the contrary, they remain unchanged in an anaerobic condition for a long time. The content of FeS_2 in the polder soils in other polders than Kojima is also much, ranging from 0.167 to 2.553%. It is shown that iron sulfides in the polder soils have a profound influence on the soil forming processes of halogenetic polder soils.

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