Considering the results we had obtained that the phototrophic N_2 fixation was greatly stimulated by the surface application of rice straw to the flooded paddy soil, the following two experiments were conducted to clarify the effective constituents of rice straw on the phototrophic N/2 fixation : (1) the phototrophic N_2 fixation in the flooded paddy soil with the addition of the treated rice straws by the WAKSMAN's proximate analysis procedure, and (2) that with the addition of organic constituents of rice straw (glucose, xylan, cellulose, lignin). The results obtained were as follows : 1. The increase of the phototrophic N_2 fixation in the flooded paddy soil with the addition of the treated rice straws was in the following order : the original rice straw > lipid extracted rice straw > soluble sugar extracted rice straw ≫ hemicellulose extracted rice straw > without rice straw (check). 2. The increase of the phototrophic N_2 fixation in the flooded paddy soil with the addition of organic constituents of rice straw was in the following order : xylan (hemicellulose) addition >_- cellulose addition ≫ glucose addition > lignin addition > without addition (check). 3. phototrophic bacteria and blue green algae were observed growing be the addition of any treated rice straw. But only blue green algae could grow by the addition of the organic constituents of rice straw, which indicated the importance of rice straw structure for the growth of phototrophic bacteria in the flooded paddy soil. 4. The contribution of each organic constituent to the phototrophic N_2 fixation was estimated to be hemicellulose 48-53%, cellulose 27-43%, glucose 0-9%, lignin <, respectively.

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The clay fraction (<2 μm) from the A and B horizon of 8 Brown Forest, 2 Yellow, 1 Red, and 2 Brown Lowland soils were treated with dithionite (DCB) and acid oxalate (pH 3.5, 90℃ ; in lab.) and the dissolved fractions were analyzed for chemical composition and by difference IR spectroscopy (DIR) for mineralogical nature. The contents of the dissolved fractions, in terms of the sum of SiO_2, Al_2O_3 and Fe_2O_3, varied from sample to sample comprising 4-23% for DCB and 3-17% for oxalate treatments. Among the three oxides, iron was most abundant, though its proportion was much less in the oxalate-soluble fractions. The ratio of oxalate-soluble to DCB-soluble iron oxides was in a range of 0.4-0.7 for most samples, suggesting that more than 50% of the free iron oxides in the soils are in "crystalline" (oxalate-insoluble) forms. Both DCB- and oxalate-soluble fractions gave IR spectra which were featureless but with weak and broad absorption bands in the regions 1100-800 and 600-400 cm^<-1>, suggesting apparently the dissolution of some layer silicates, besides iron oxides. However, the spectra lacked the absorption band in the region > 3500 cm^<-1> due to OH-stretching, which would have appeared if the layer silicates were dissolved in significant amounts. Moreover, the silica/alumina molar ratios of the oxalate-soluble fractions were in the range of 1.3-1.8, being too low to ascribe these oxides to the dissolution of the layer silicates. These results indicated that the source of the oxalate-soluble silica and alumina was not in the layer silicates themselves, but in some other "noncrystalline" materials associated with them. Since the original clay samples did not contain allophane and imogolite, we assume that such "noncrystalline" materials are a part of layer silicates which has been decayed severely by weathering to an extent that shows noncrystalline properties.

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Konsen district, eastern Hokkaido, Japan is characterized by frigid soil temperature regime and dairy farming. We classified 6 representative volcanic ash soils from the district according to the last Keys to Soil Taxonomy (Soil Survey Staff, 1990) and studied the applicability of this classification to understand fully relationships between the soil and between the soils and the factors responsible for their characters. We also compared the soil classification according to the last Keys to Soil Taxonomy with those obtained by two domestic soil classification systems. It was shown that both the last Keys to Soil taxonomy and Hokkaido soil classification for agricultural land are most useful and they show close correlation between the two classification as follows.

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Photosynthesis and evapotranspiration rate of rice plants raised with and without silicate in a growth chamber was compared. Photosynthesis rate determined using an infra-red CO_2 analyzer was higher in the silicate-supplied plants. Apparent stomatal conductance was higher in the silicate-deprived plants ; however, greater evapotranspiration through cuticle-layer contributed to the exaggerated stomatal conductance, and actual stomatal conductance was calculated to be greater in the silicate-supplied plants. As the photosynthesis rate determined in terms of oxygen evolution by the leaf discs was nearly the same between the treatments, the greater stomata conductance contributed to the higher photosynthesis rate in the silicate-supplied rice plants. Consequently, it was concluded that silicate accumulation in the leaves prevented water-loss through cuticle-layer, then provided favorable water-relations for photosynthesis.

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Allelopathy of common lambsquarters (Chenopodium album) has been reported. It was found that crude extracts of plant leaves or residues have inhibitory activity to other plant germination and/or growth and that root exudates collected from the solution culture of lambsquarters also reduce other plant growth. So we assembled stairstep experiment apparatus, a sort of sand culture, connecting the pot with pipe so that root exudates of one plant can flow into another plant, and CRETS (continuous root exudates trapping system) and used them for the discrimination of allelopathy. The results showed that common lambsquarters cultivated in stairstep apparatus and CRETS inhibit the growth of cucumber plant. In both cases, the inhibition of upper part of the cucumber plant was more prominent than that of roots. These results show that growth-inhibiting effect of common lambsquarters in the mixed culture with cucumber plant is not attributed to the competitions for light and nutrients but to allelopathic interference. In CRETS test, XAD-4 resin could eliminate the inhibitory activity of common lambsquarters to cucumber plant. The crude extract of XAD-4 resin, to which the phenolic exudates of common lambsquarters was trapped, also contained plant growth-inhibiting activity. We concluded that common lambsquarters have an allelopathic potential by their root exudates.

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Allelopathic interaction by plant root exudates was discriminated with rotary greenhouse experiments and stairstep experiments, which eliminate the competitions for light, water and nutrients. With rotary greenhouse experiments, cucumber was the most sensitive to other plant exudates in these mixed culture conditions. The most effective plant to reduce plant growth was velvet bean (Mucuna pruriens), followed by fingergrass (Digitaria sanguinalis) and common lambsquarters (Chenopodium album). Velvet bean reduced the growth of cucumber plants, but had little effect on kidney bean. With stairstep experiments n the combination of velvet bean and lettuce, velvet bean and kidney bean, velvet bean reduced the growth of lettuce, especially root growth, but did not affect the growth of kidney bean. The results obtained by these tow methods were identical. In the germination and seedling growth tests, velvet bean root exudates collected from the medium of solution culture inhibited the growth of lettuce and cucumber, especially radicle elongation, but had little effect on other plants, and rather stimulated the growth of many graminaceous plants such as timothy, redtop, burmudagrass. We concluded that velvet bean has an allelopathic potential by its root exudates. Though the growth of some plants was reduced by the root exudates of velvet bean, some graminaceous plants had little effect by the same solution.

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Effects of macronutrient cations -K, Ca and Mg- on uptake of Cd in whole rice plants were examined to compare them with the antagonistic effect found in the rice radicles previously. The plants were grown in culture solution with Cd and the cations of various concentrations. From early tillering stage to flowering stage, the growth rates of Cd-treated plants were as high as those of untreated plants, and concurrently with the growth, increase of the uptake of Cd and the cations was high. During this period, the effect of the cations on uptake of Cd was found to be the reverse of that in the radicles, and the cations in media finally showed synergistic effect on Cd uptake in the whole plants. Increase of Cd uptake was observed in accordance with increased uptake of the cations which was induced by increase of concentration of the cations in media. High positive correlations were shown between content of Cd and those of divalent macronutrient cations in the aerial parts. Therefore, there exists a parallelism between translocation of Cd and those of the cations. Cumulative amounts of transpiration in this period were not parallel to those of Cd. From these results, we judged that Cd was translocated by exchange adsorption with macronutrient cations on inner surface of xylem vessels. Thus, we assume that the synergistic effect found in this work should be brought about through the exchange adsorption in xylem vessels which developed concomitantly with plant growth, because in the exchange adsorption the translocation of Cd must necessarily be accelerated with increased uptake of the cations by higher cation treatments.

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Source-sink relationship in photosynthates of the potato plant was studied by observation of vascular system and ^<14>C-tracer method. 1) The vascular system of the stem is composed of five bundles, and the exsertion point of leaves alternates with a 2/5 phyllotaxy. Organs, which are exserted from a node, can be classified into 5 groups by the phyllotaxy. 2) ^<14>C assimilated by a leaf at a node translocates more intensively to the organs exserted from that node group, and the 2nd and 3rd node groups above or below the ^<14>C-fed leaf than other organs, supporting the morphological observation. However, actively growing organs receive photosynthate from the leaves belonging to other vascular systems to some extent depending upon the situation of source-sink relationship. 3) ^<14>C assimilated by each leaf was mainly translocated to leaves, branches above ^<14>C-assimilated leaf, and roots at the 10th leaf stage, to branches and stem near the ^<14>C-assimilated leaf at flower-bud-appearing stage, and to tubers at flowering of 2nd flower. Thus, after tuber began to swell, ^<14&g;C-assimilated by each leaf almost translocated to tubers so that mutual relationship to some organs among leaves like rice plant was not clear in potato plant.

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The productivity of maize and potato is high in comparison to other crop because of high photosynthetic activity and of high harvest index, respectively. These two crops were grown in a field without and with 300 kg N/ha of nitrogen application, and the behavior of carbon and nitrogen during ripening was studied. The results obtained are as follows : 1) When the demand of the harvesting organs for photosynthate exceeds the photosynthetic rate during ripening, carbon compounds in the leaves and stems are reutilized (respired or retranslocated). 2) During ripening, the photosynthetic rate exceeds the demand of harvesting organs, the decrease of shoot dry weight is negligible, and the content of sugar and starch in the stem is kept considerably high till the end of growth in maize. On the other hand, in potato, as the demand of harvesting organs for photosynthates exceeds the photosynthetic rate, the decrease of the shoot dry weight is remarkable, and not only sugar and starch, but also cellulose and hemicellulose in the leaves and stems are reutilized. 3) The nitrogen accumulated in harvesting organs can be divided into (a) nitrogen absorbed from the roots during ripening, and (b) that retranslocated from the shoot. If the demand of harvesting organs for nitrogen exceeds the rate of nitrogen absorption by the roots, the retranslocation of nitrogen from the shoot is stimulated. 4) In maize, as the photosynthetic rate is kept high during ripening, the ability of roots to absorb nitrogen is kept high, and the retranslocation of nitrogen from the shoot is limited. In contrast, in potato, as the demand of tubers for nitrogen is larger than the nitrogen absorption rate of roots, the retranslocation of nitrogen from the shoot to the tubers is large, and this retranslocation results in a decrease of the photosynthetic rate of leaves. 5) The amount of ethanol soluble-N (mainly amides) in harvesting organs is large and increases with an increase of nitrogen application in potato, whereas in maize, it is low and is not affected by nitrogen application. Therefore, potato tubers require a large amount of nitrogen when nitrogen is applied. 6) The composition of free amino acid of the leaves, stems and harvest organs is similar regardless of nitrogen application, and that of stems is similar between the two crops. The composition of protein amino acids is almost constant regardless of organs, crops, and nitrogen application. Thus, the mechanism of reconstruction of the nitrogen compounds from in the shoot into those in the harvest organs is almost the same in both crops.

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The relationship between the uptake of nutrients (N, P, K, Si, Ca, Mg, Fe, Mn, Na) and the yield components (brown rice, abortive grain, rice screenings, 1,000-grain weight, % filled spikelet, panicle number, spikelet number per panicle) was analyzed using 4 rice varieties at 3 districts of Japan. The weight of abortive grains was connected with P absorbed in the tillering stage and Na % in the leaf and stem at the panicle formation stage. The weight of rice screenings was connected with N %, P % , Ca % in the rice straw at the maturing stage. The yield components of rice varieties in the cold northern districts had relationship to the nutrient uptake in the early growth stage. These results indicate that the growth of rice in the early stage is important in these northern districts. But in the rice varieties of the south-western districts, the yield components had relationship to some nutrients absorbed in the vagetative-lag phase. These results suggest that the nutritive conditions in the vegetative-leg phase are very important components for the rice crop production in these warm districts. The strongest correlation was observed between the yield component and the nutrient which has something special about the content in the soil or the rice plant. Sodium had a negative correlation with the abortive grain weight in the northern districts, and a positive correlation with a grain number per panicle in the south-western districts. These results suggest that sodium is effective on the yield components of rice.

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