Japanese Journal of Soil Science and Plant Nutrition

1. To separate P^<32> from Ca^<45> we devised a method, depending upon making use their difference in β-ray energy. According to this method, P^<32> and Ca^<45>, when existed at the same time in one plant, could be traced independently, individual difference of plants being eliminated. 2. By this separation method, translocation and distribution of P^<32> and Ca^<45> in soy-bean plant were examined, and we found that the translocation rate of "Ca" was slower than that of "P", but "Ca" was translocated, as time elapsed, to the upper leaves. 3. It was concluded, therefore, that distribution and translocation of "P" would be dependent on the metabolic factors, i. e. respiration and photosynthesis. On the other hand, those of "Ca" would be dependent rather on non-metabolic factors such as exchange and diffusion. 4. In the field, the first hunger signs of "N", "P", "K" etc. usually appeared in upper leaves, while those of "Ca", "Fe", "B" etc., in lower leaves. This phenomena was possibly due to the difference of translocation rate in the plant of each nutrient.

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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.

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The purpose of our studies is to investigate the reasons why the crop yield in regions where a transferring cultivation between paddy and upland fields is practiced, is always greater than that in a region where the rice plant is the only crop. Samples of soil are four different types; peat, muck, clay and sandy soils as the same in Part 1. Permeability and temperature of soils, content of FeO, base exchange capacity and content of total and organic nitrogen were determined. The following results were obtained. 1) Permeability of the soil in the transferring fields is greater than that in the one crop paddy fields, because the better soil granular structure is made in the transferring cultivation field. Almost no difference of temperature was between two soils, the paddy field and the transferring cultivation field as shown in Table 3. 2) Content of FeO, total, nitrogen and base exchange capacity, in May, are higher in the transferring cultivation field than in the paddy field. Content of easily decomposed organic nitrogen, in July, has the same result. These results are given in Table 2,4,5 and 7. 3) Contents of NO_3-N in May and NH_4-N in July and September were measured. Rate of availability of N to the rice plant in the transferring cultivation field is more or less slower than in the one crop paddy field, but the efficiency of N is higher than in the one crop paddy field. 4) The reason why the yield of rice plant in the transferring cultivation field is greater than the paddy field, will be explained as that primarily physical soil structure is good for the rice plant, and secondarily efficiency of available N becoms higher.

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The author distinguished three stages in the growth of rice plat, viz., the 1st stage is from the germination to the ear forming, the 2nd stage is from the ear forming to the flworing and the 3rd stage is after flowering. Three stages of growth are chiefly connected with the function of leaves 3/0〜5/0,6/0〜9/0 and 10/0〜12/0 respectively. To make clear the physiological bases of these characteristic functions of leaves, the characteristics of nitrogen metabolism of these leaves are studied first. The present report embodies results of these studies. The following results were obtained from them. 1) The total amount of nitrogen in each leaf increases accompanying with the growth of that leaf, and, after reaching to the maximum value, it decreases. The time when the maximum nitrogen accumulation in a leaf is attained, comes in sequence from lower leaf to upper leaf as indicated in Fig. 4. Periods between the peak of the curve of the nitrogen fluxion of one leaf and that of the next leaf are not constant. Specifically, in leaves 3/0〜5/0 the periods are almost the same; in 6/0〜9/0 nitrogen begins to accumulate from lower leaves first, then to upper ones, but it does not outflow from these leaves until earforming stage. Then the nitrogen in all leaves decreases at the same time and nitrogen accumulates in spikelet and stem simultaneously; in leaves 10/0〜12/0 nitrogen begins to accumulate from lower leaves to upper ones. After the flowering stage nitrogen in these leaves begins to flow out and accumulates in ear synchronously. 2) Translocation quotients of nitrogen (as shown in Table 3) differ by the position of the leaf, In the case 3/0〜5/0 it shows about 50%, in the case of 6/0〜9/0 it shows 70%, and in the case of 10/0〜12/0 it reaches to 75%. 3) In the 1st stage of growth, the nitrogen contents of leaves at upper position are higher than that of lower ones, but in the 2nd stage of growth, nitrogen contents of leaves at any position are almost the same. 4) Leaves 3/0〜5/0 have characteristic connection to tillering. As far as the nitrogen metabolism is concerned, it is not reasonable to consider that a tiller at any position becomes independent receiving its nitrogen supply from the stored in the leaf at the same position. But substances assimilated by a leaf accelerate nitrogen absorption and the nitrogen thus absorbed goes up to the tiller at the same position.

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