We investigated the burning process of Susuki plants at various temperatures (150, 200, 250, 300, 350, 400 and 450℃) giving special attention to the elementary composition and humus composition. (1) When the Susuki samples (non-heated samples) were heated at 150 and 200℃, the samples were not burned and changed to brown in color due to heat applied (non-burned samples). At the temperature of 250℃ or higher, the samples were burned, and consequently charred residues and ash were produced (burned samples). (2) The ratios of amounts of dry material, carbon, hydrogen and oxygen remaining in the heated samples, as compared to those originally present in the non-heated samples, were much lower in the burned samples than in the non-burned samples. Such a relationship was not found for nitrogen or ash. (3) The results of an elementary analysis indicated that the carbon content (ash-free oven-dried basis) tended to increase with the increase of heating temperature, but the reverse was true for oxygen content. There was no regular relationship between the hydrogen and nitrogen contents and the heating temperature. The atomic [H]/[C] and [O]/[C] ratios in the burned samples were much lower than those in the non-burned and non-heated samples. The burning process of Susuki plants was mainly arranged in the direction of dehydration on the [H]/[C] versus [O]/[C] diagram. (4) The results of humus analysis indicated that the extracted humus, humic acid and fulvic acid contents (ash-free oven-dried basis) in the burned samples were much lower than those in the non-burned samples. There was no relationship between the total humus content and heating temperature. (5) The humic acids extracted from the non-heated and non-burned samples were of the Rp type. The humic acids in the burned samples were A type, and the amount of acid decreased with the increase of heating temperature.

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The purposes of this investigation are to clarify the production of vitamin B_<12> active substances by rhizobia and to examine their localization in the plant parts of some legumes as related to their nodulation by the Euglena bioassay method. The results obtained are as follows. 1. All of the rhizobia tested had the ability to produce B_<12> active substances. However, no significant correlation existed among the species of rhizobia. 2. The production of active substances markedly increased with the increase of cobalt concentration in the culture medium. The Rhizobium meliloti and Bradyrhizobium japonicum tested in this experiment required more than 1 mg L^<-1> of cobalt chloride for the maxium production of B_<12> active substances. The application of nitrate to rhizobial culture medium slightly enhanced the production of B_<12> active substances. 3. The larger part of B_<12> activity in the culture media of R. meliloti and B. japonicum was found to depend on cobalamin by paper chromatography. 4. A higher concentration of B_<12> active substances was detected in the bleeding sap of nodulated kidney bean as compared to the non-nodulated one. 5. The concentration of B_<12> active substances was higher in the underground part than in the aerial part, and the tendency was more clearly observed in nodulated lupin plants than in non-nodulated lupin plants. 6. The greater part of B_<12> active substances in nodulated plants was present in the nodules of the leguminous species tested in this experiment. The concentration in the nodules was about 10 to 60 times highe than that in the root and about 100 to 700 times higher than that in the aerial parts. However, the concentration in soybean nodules fluctuated largely with the age of the plant.

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Five snow samples collected on Mt. Hachimantai (1400 m a. s. l. ) in the months of May and June from 1991 to 1996 contained significant amounts of eolian dust. Fifty-four rainwater samples were collected at Morioka from Jan. 17, 1992 to Apr. 27, 1994 and at Fukaura from Sept. 28, 1992 to Feb. 3, 1995 ; areas located in Northeast Japan. The pH values, concentration of chemical components, and amount of eolian dust in the rainwater samples were determined. Fifteen percent and 27% of the rainwater samples from Morioka and Fukaura, respectively, were acid rain. About 76 and 57% of the inorganic dust deposits in the rainwater samples from Morioka and Fukaura, respectively, were dominated by a <20 μm fraction and their depositions were marked from winter to spring, suggesting a strong influence of Asian long-range eolian dust. The annual deposition of nssSO_4^<2-> and nssCa^<2+> in rainwater was 4.5 and 4.0 meq m^<-2> in Morioka and 6.2 and 7.1 meq m^<-2> in Fukaura, respectively. The chemical compositions of eolian dust deposits in the rainwater samples were compared with Chinese loess and Hachimantai eolian dust in snow deposits. These deposits were characterized by almost the same chemical, physical and mineralogical properties. Sulfate in the Morioka rainwater is transported from China. In addition, the relatively low E factors of SO_4^<2-> of Japanese rainwater samples were partially influenced by sea salt, especially in the winter season. A significant correlation between the amounts of nssSO_4^<2-> and nssCa^<2+> of eolian dust deposits in rainwater samples suggests that nssSO_4^<2-> and most of the nssCa^<2+> and nssK^+ were dissolved from Asian long-range eolian dust contained in the rainwater samples. The annual deposition of nssSO_4^<2-> and nssCa^<2+> in Northeast Japan was 1.5 to 2 times higher for nssSO_4^<2-> and 3 to 5 times higher for nssCa^<2+> than that in Southwest Japan. The present results suggest that the rainwater samples in Northeast Japan are strongly influenced by Asian long-range eolian dust.

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Concentrations of nssF^-, nssSO_4^<2-> and nssCa^<2+> in 94 rainwater samples collected at Yashiro, Hyogo Prefecture, Morioka, Iwate Prefecture and Fukaura, Aomori Prefecture, Japan, were determined and correlations between nssF^- and nssSO_4^<2-> or nssCa^<2+> concentrations of the rainwater samples were analyzed. The origin of chemical species (X) was discussed using the enrichment factor (E) as defined by E=(X/Na)rainwater/(X/Na)seawater, where Na^+ is used as the reference element for sea salt. In Yashiro, Morioka and Fukaura, the E factors of SO_4^<2->, Ca^<2+> andF^- were lower in the Kosa period (dust event in Japan) (Dec. to May) than the non-Kosa period (Jan. to Nov.), indicating large amounts of sea salt were incorporated into the rainwater by a seasonal wind in the Kosa period. In Fukaura, which is located in the near Japan Sea coast, much lower E factors were observed under the strong influence of sea salt than in Yashiro and Morioka, which are inland areas. There were highly significant correlations between nssF^- and nssSO_4^<2-> or nssCa^<2+> concentrations. Consequently, these chemical species in Japanese rainwater saples are of aerosol (eolian dust and coal soot) origin, transported from the Asian Continent.

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To clarify the effect of nitrogen (N) cultural practices on N-use efficiency for the total number of grains produced per amount of N in a plant heading (NUE for G/N), a field experiment was carried out. Furthermore, the effects of translocation of top-dressed N applied at different dates and the amount of total available carbohydrate (TAC) in the plant at heading on the protein content in milled rice was evaluated. The results obtained were as follows. 1. No significant differences were observed in the number of differentiated grains among the application times of top-dressed N and shading treatments. However, the number of degenerated grains was affected by both top-dressed N timing and shading. A delay in the application date of top-dressed N and increase of shading percentage resulted in an increase in the number of degenerated grains. 2. Nitrogen-use efficiency as affected by the date of N application (day before heading, DBH) was higher in the order of 26 DBH > 19 DBH > 16 DBH > 9 DBH > 5 DBH. Furthermore, increasing the shading percentage decreased N-use efficiency. 3. Delaying the date of top-dressed N induced the reduction of N-use efficiency and an increase in the amount of N per grain, resulting in an increase of protein content in the milled rice. The protein content of milled rice was also affected by the amount of N derived from top-dressed N, which was governed by application timing. 4. The low NUE for G/N controlled by shading treatment resulted in an increase in the amount of N in grains and in the protein content of the milled rice. The amount of TAC in a plant at heading, as regulated by shading treatment, affected the protein content through grain weight.

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The purpose of this research is to improve the surface properties of allophane and imogolite which are frequently included in volcanic ash soils. Allophane and imogolite were respectively separated from the inner part and outer part of weathered pumice grains. These materials were treated with NH_4F solution. Surface acid strength and cation exchange capacity (CEC) were measured before and after the treatment. The measured values of CEC increased with the increasing concentration of NH_4F solution. The maximum values of the treated materials were 3 to 4.5 times higher for allophane and 22 times higher for imogolite than those of their untreated counterparts. The surface acidity measured by the Hammett indicator method was much stronger for allophane and imogolite treated with NH_4F solution than for those without treatment. The mechanism of the changes in CEC and surface acidity analyzed by infrared spectroscopy and molecular orbital method were as follows : Silanol groups (Si-OH) in the structures of allophane and imogolite interact at the electron level with fluorine taken into the structures. This interaction facilitates the dissociation of protons from the silanol groups, causing the enhancement of CEC and a strengthening of the acidity.

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A dynamic model that mainly includes chemical reactions taking place in the soil was developed to simulate the soil acidification triggered by acidic deposition. The model was applied to soil acidification experiments in order to confirm the applicability of the model and to evaluate the contributions of each buffering mechanism. In the experiment, pH adjusted sulfuric acid was added to twelve soil samples for four years. In case of the simulated acid rain with pH3, the estimated temporal change of soil chemistry corresponded well with the measurements except for exchangeable aluminum. Selectivity coefficients of cation exchange showed a clear positive correlation with the soil pH for each soil sample, and change in exchangeable aluminum could be predicted by expressing selectivity coefficients as a function of soil pH. According to the results of the model estimation, the main buffering mechanisms were Al hydroxide dissolution and/or release of exchangeable base cations, and acid was neutralized mainly in the surface soil layer (10 cm) by these processes. For the acid rain with pH4, decreased rates of exchangeable base cation were sometimes less than the observed ones. This disagreement was considered to be caused by the uncertainty of the data on mineral weathering and nitrification rates.

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The farmlands (upland crop fields, drained paddy field for upland crops, reclamated upland field) and forested area in the vicinity were surveyed in correspondence with the Shimanto Belt, Chichibu Belt and Sambagawa Belt in Kochi Prefecture, Japan. The soil fertility in each belt was evaluated using the general and inherent properties of the soils, such as oxide contents, zero point of charge (ZPC), and clay mineralogy, which have not been often included in soil evaluation so far. Based on these data, the factors affecting ZPC and rrp were extracted by statistical analysis. In the Shimanto Belt, land reclamation was conducted widely, resulting in immature soils with both poor physical and chemical soil properties. Improvement of the soils could be accomplished only by continuous soil management. The amount of Fe and Al oxides as variable charge fractions and lime application caused a higher shift in ZPC, while the higher content of organic matter and presence of permanent negative-charged clays caused a larger σ_p. In the Chichibu and Sambagawa Belts, drained paddy fields for upland crops were distributed widely. Although improvement in the permeability due to aggregation in the surface soils was observed, subsoils had not yet been improved in terms of both permeability and retention of water due to remnant properties of the former paddy fields. Exchangeable cations derived from permanent materials caused a higher shift in ZPC, while organic matter and permanent negative-charged clays caused a larger σ_p value, the same as the reason for the soils in the Shimanto Belt. In all the soils used in the study, the application of lime brought a higher shift in ZPC value for the surface soil, while exchangeable cations derived from parent materials made it higher in the subsoils. The higher content of organic matter added naturally and/or artificially application made the value of ep higher in the surface soils, and permanent negative-charged clays made it higher in the subsoils.

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Rice plants were water-cultured with a combination of aluminum (0, 0.2, 0.8 mmol L^<-1>) and silicon (0, 3.0 mmol L^<-1>) in a 0.5 mmol L^<-1> Ca(NO_3)_2 solution, and both elements with different chemical forms in the plant organs were determined to evaluate the effects of silicon supply on the amelioration of aluminum injury to the plants. This culture solution was renewed every day during the treatment period (4 d). Plant growth, especially root growth, decreased with the increase of aluminum (Al) concentration in the culture solution, but the silicon supply alleviated plant growth. Total Al, water-soluble polymer Al and water-insoluble polymer Al contents in the roots and leaves tended to increase more in the presence of silicon than in the absence of silicon, and water-soluble monomer Al content in the leaves decreased. These results suggest that the ameliorative effects of silicon on aluminum injury to rice may be attributed to ; (1) growth improvement by silicon itself, (2) a decrease in aluminum concentration due to silicon in the culture solution and (3) the alteration of aluminum chemical forms in solutions and plants by silicon, resulting in a decrease in aluminum toxicity.

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Twelve strains of Rhizobiurn sp. (Phaseolus) isolated from different soils in Tokachi, Japan, were inoculated to common bean (Phaseolus vulgaris L. ) cv. Hokkaikintoki cultured on artificial vermiculite with liquid medium of different NO_3^--N levels. When high (30 ppm N) and low (5 ppm N) levels of NO_3^--N were supplied, the difference of each parameter was related to that nodule number : both 2.0 times; dry weight per one nodule : 1.8 and 2.7 times ; acetylene reduction activity (ARA) : 3.8 and 4.8 times ; specific ARA : 4.0 and 3.3 times, respectively. The differences of plant growth and plant nitrogen concentration were not beyond 2.0 times. The species of four beneficial strains, NOKO-313 had stable and high nitrogen fixation ability (NFA) regardless of NO_3^--N concentration, NOKO-311 indicated high NFA though its activity was not inhibited by high NO_3^-N level, NOKO-312 had medium NFA and its activity declined quickly during the symbiotic period with common bean, and NOKO-314 formed many nodules under low NO_3^--N level, were identified using phenotypic and genotypic characteristics. Two strains, NOKO-312 (DDBJ Accession No. AB008310) and NOKO-313 (AB008311), belonged to Rhizobium etli, and the other two, NOKO-311 (AB008309) and NOKO-314 (AB008312) were R. legurninosarum by. phaseoil. Another beneficial strain, NOKO-301 (AB008308) isolated from Andosol soil in Fuchu, Japan, belonged to Rhizobiurn etli.

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Hachirou-gata is the secondary largest lake in Japan following Lake Biwa. In 1957, the "National Hachirou-Gata Reclamation Project" was started, and the entire project was completed in 1967. Out of 22, 024 ha in Hachirou-gata, reclamation land totalled 17,239 ha. The drainage inside the central area is pumped out by a central canal and north and south pumping stations constructed at both ends of the canal. The phosphate concentration of the drainage of the south pumping station was 0.47mg L^<-1>, and was more than 3 times higher than that of the north pumping station. We investgated the cause of this difference. The results obtained were as follows. We measured the phosphate concentrations of the drainage of 40 first class branch drainage canals and the highest concentration was 1.62 mg L^<-1> at Right 3 Station (LD-G1). This branch drainage canal flowed into the main drainage canal beside the south bridge; for that reason the phosphate concentration of the drainage of the south pumping station was higher than that of the north pumping station. Then, we investigated the water in the small canals which were around branch drainage canal LD-G1, and many of them showed higher concentrations of phosphate. The water which flowed in these small canals originated from the bottom of these canals.

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