Fused potassium silicate fertilizer was produced with steelmaking slag and additional potassium carbonate in the steelmaking process. In order to evaluate the availability of slow-release potassium, solubility and crop response were investigated using three type of fused potassium silicate fertilizers which had different solubility. In the soil column experiments, potassium contained in fused potassium silicate fertilizers was released in very slow form compared with potassium sulfate, though W-K_2O of fused potassium silicate fertilizer was relatively high. Eluviation quantity from fused potassium silicate fertilizer was much lower than from potassium sulfate. Response of crops showed fused potassium silicate fertilizer, which contained relatively high amounts of W-K_2O, in terms of the growth and the dry matter production, to be as effective as potassium sulfate. As for the amount of potassium uptake of Chinese cabbage, potassium sulfate showed the highest value; however, the dry matter production of potassium sulfate was almost same as for fused potassium silicate fertilizer. These results indicated that fused potassium silicate fertilizer could supply potassium in slow form to crops and result in effective utilization by crops.

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A soil database has been created based on soil maps (soil map database) and soil survey information (soil information database) using a general purpose geographical information system and database software on a personal computer, and examples of application of this database are introduced. 1. In the soil map database, a polygon showing boundaries of agricultural land is distinguished by soil division authorized by the prefecture concerned. Soil classification information, and the latest information on physical and chemical characteristics of plowed soil obtained from a survey made at about 550 points are used as information for its attributes. 2. Drawing of a soil map such as a CEC distribution diagram that is based on the polygon attributes information, and area aggregation are made easy after the soil map information is integrated into a geographical information system. 3. Photographs showing section, geologic column and compactness distribution diagram are integrated into the soil information database together with characteristics of the soil, and physical and chemical characteristics information for plowed soil and next layer soil to allow a visual understanding of soil condition down to the substratum (about 80 cm deep). 4. After the soil map and soil information database are converted into image data, a cultivated field soil information database is created by HTML. It is now possible to retrieve soil distribution and current soil condition with ease.

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Effects of the single basal application of controlled availability fertilizers (CAFs) on growth, yield and fruit quality of tomato plants were studied in comparison with conventional rapidly availability fertilizer. 1) CAFs plots were divided into two types corresponding to even releasing plot and middle and latter stage releasing plot which were designed by blending CDU compound fertilizer and three sigmoid types of polyolefin coated fertilizers (POCFs) with the different releasing type. 2) There was no difference in width or length of leaves or diameter of stems of tomato plants between the single basal application of CAFs plots and conventional plot. 3) Total fruit yield of tomatoes in the middle and latter stage releasing plot was superior to that in the conventional fertilizer plot. Yield of Grade A (good shape, 100g<) for the middle and latter stage releasing plot was superior to those in the conventional plot and in the even releasing plot. 4) There was no difference in contents of soluble solids (Brix %) or ascorbic acid of tomato fruits. 5) From the results mentioned above, the labor saving cultivation of tomatores by a single basal application using several kinds of sigmoid type CAFs without any decrease in either yield or quality of tomato fruits is highly feasible.

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We examined the effects of 3 rare earth elements (La, Sm and Yb) on germination of plants and AM colonization. In addition, the effects of 3 rare earth elements and arbuscular mycorrhizal (AM) colonization on plant growth were examined by a pot experiment. The results are summarized as follows.1) The effects of rare earth elements on germination were investigated by comparing the root length of germinated seeds of marigold (Tagetes patula L.), onion (Allium cepa L.) and tall fescue (Festuca arundinacea Schreb.) in quartz sand treated with La, Sm and Yb. The root length of all the plants was markedly lowered by the addition of La, Sm and Yb at the rate of 100μmol kg^<-1>. At the rate of 10μmol kg^<-1>, although the root length of marigold was not lowered, those of onion and tall fescue were slightly lowered by the addition of Yb and Sm, respectively. From the results above, it is suggested that the addition of La, Sm and Yb at the rate of 10 or 100μmol kg^<-1> probably causes the inhibition of germination. 2) The effects of rare earth elements on AM colonization were examined by use of marigold colonized by Glomus etunicatum. We found that AM colonization of marigold root was not inhibited by the addition of La, Sm and Yb at the rate of 10μmol kg^<-1>. 3) To examine the effects of AM colonization and rare earth elements on plant growth, mycorrhizal (AM fungus ; Glomus etunicatum) and non-mycorrhizal marigolds were grown for 50 d in river sand with or without application of La, Sm and Yb at the rate of 10μmol kg^<-1>. The growth of non-mycorrhizal marigold, especially aerial parts, was inhibited by the addition of La and Yb. However, the growth of mycorrhizal marigold was not inhibited by the addition of La, Sm and Yb. Therefore, AM colonization would be attributed to the amelioration of phytotoxicity of La and Yb.

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Filamentous acetate-utilizing methanogens were isolated from several samples of Japanese paddy field soil and their characterization and distribution were investigated. With Kanagi soil from Aomori Prefecture, the filamentous acetate-utilizing methanogens in submersion numbered 10^4 MPN g^<-1> dry soil and 10^3 MPN g^<-1>dry soil in the drainage stage. The filamentous acetate-utilizing methanogen numbers were one-twenty-sixth that of coccoid acetate-utilizing methanogens in the flooded stage and one-seventh that in the drainage stage. Research allowed selective accumulation of filamentous acetate-utilizing methanogens by repeated culturing in a mineral medium with acetate so that these methanogens could be isolated by an agar shake method. The filamentous acetate-utilizing methanogens lived in the filamentous cell state and elongated in the plant residues and soil particles taken from paddy soil in submersion. When the plant residues and soil particles were incubated with an acetate medium, higher numbers of bacteria, fungi, and filamentous methanogens were observed on the plant residues than on soil particles. As filamentous acetate-utilizing methanogens were not observed in soil water, the organisms seem to survive by adhering to the plant residues and soil particles. Strain K-5 isolated from a Kanagi paddy soil formed short filaments that consisted of 2-7 rod-shaped cells and exhibited a blue-green auto-fluorescence. Results from the electron microscopy of a thin section of a strain K-5 cell clarified that it has a sheath of 2 layers with intense electron density on the outside of the cell membrane. The strain did not die out immediately even when it was exposed to oxygen. However, the desiccation of the cell suspension of strain K-5 in air resulted in a strong reduction of the potential acetate consumption and methane production. Filamentous acetate-utilizing methanogens were isolated from 5 samples of paddy soil from the Hokkaido region to the Kyushu district. These results indicate that filamentous acetate-utilizing methanogens live throughout paddy field soil in spite of the difference in temperature and differing physicochemical properties of paddy soil.

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The application of charcoal to the soil has a number of effects on the soil's chemical, physical and biological properties. Soil conditioning with charcoal sometimes results in improved crop yields, although at present it is not known which characteristic of charcoal promotes plant growth. This study was performed to investigate the degree to which charcoal retains nutrients, including nitrates. Two kinds of charcoal, made from Larix kaempferi (Japanese White Larch) and Quercus phillyraeoides (Ubame Oak) were employed. Conclusions obtained are summarized as follows. 1) The porosities of L.kaempferi charcoal and Q.phillyraeoides charcoal were 69% and 31% respectively. The median pore size of L.kaempferi charcoal was larger than that of Q.philly-raeoides charcoal. 2) The amount of nitrate adsorbed by the two charcoals was investigated as a function of pH. Nitrate adsorption by both charcoals increased with reduced pH, but at the same pH, nitrate adsorption by Q.phillyraeoides charcoal was greater than that of L.kaempferi charcoal. 3) The release of nitrate from 2-4 mm-diameter charcoal pellects presaturated with 10 mmol L^<-1>KNO_3 was analyzed to evaluate the nitrate-retentive ability of granulated charcoals. Greater amounts of nitrate were retained in L.kaempferi charcoal than in Q.phillyraeoides charcoal. 4) The movement of nitrate in charcoal-added soil columns was investigated. The amount of nitrate retained in the upper part of the column increased with addition of charcoal to the soil.

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The degree of hardening by air-drying of 43 samples of Maji-soils (yellow soils, red soils and dark red soils) in the central region of Okinawa Island was determined by an unconfined compression test. Physical and chemical analysis was also conducted for the same samples, and the relationship between the degree of hardening and physical and chemical properties was investigated. The degree of hardening, i.e.unconfined compressive strength, in air-dried state varied among the examined soils. The maximum was 6.4 MPa and the minimum was 0.6 MPa. Clay content, pH and exchangeable calcium content were intimately related to the degree of hardening.Clay content showed a positive relationship to the degree of shrinkage of soil blocks by air-drying. It seems that clay content affects the degree of hardening through the degree of shrinkage. Soil pH and exchangeable calcium content were positively related mutually, and both showed a positive relationship to the degree of hardening. However pH was not related to the degree of shrinkage. Amendment of alkali solution (Sodium hydroxide) or exchangeable cations (calcium, magnesium, potassium or sodium) increased the degree of hardening of an acidic soil. The degree of shrinkage was also increased by amendment of exchangeable cations, but it was not increased by alkali solution amendment. Fine particle size distribution examined by a laser scattering method and clay mineral composition showed no difference among the soils with different pH. Consequently, it is assumed that pH affects soil hardening through some physicochemical condition of the surface of soil particles, such as charge, that affects the microstructure of floc of soil particles, and exchangeable calcium fosters the shrinkage by air-drying and thus it increases the degree of hardening.

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The concentration changes of nitrate nitrogen (NO_<3->N) and other ions were examined in 4 springs called "Shohzu" of Konomoto Alluvial Fan and the water of Takinami River in Ohno Basin, Fukui Prefecture. The outline of results is as follows : The waters of these springs and the river were supplied from the same source, judging from the measurement of lead isotope ratios and the results of previous studies. The concentrations of NO_<3->N and other ions in these waters were quite low, in spite of a little pollution from fertilizer applications. The NO_<3->N concentration increased relatively between Konomoto-yakushido spring located at the top of fan and Shinokura-jinja upstream of an urban area, and many fields distributed between them. Its concentration in the latter spring increased a little in July when midsummer drainage is carried out in rice fields and fertilizers are applied to upland crops, and in October to November at the time of drainage after rice cultivation. The changing pattern of NO_<3->N concentration coincided with that of sulfate, a component of fertilizers, at Shinokura-jinja spring. This suggested that the fertilizer application in fields had a small effect on ground water. The concentration changes of NO_<3->N and other anions in Nakano-shohzu downstream from the urban area, where small fields are scattered, were similar to those of Shinokura-jinja spring. In O-shohzu, within the urban area, the ion concentrations were hardly different from those of Shinokura-jinja spring located at the upper end of the groundwater system. On the other hand, the seasonal changes of NO_<3->N concentration were very small, and might have been caused by the installation of pavement and sewerage.

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Nitrogen use efficiency (number of grains/amount of N in rice plant at heading) and grain weight affected protein content of milled rice. Topdressed N might contribute to protein content of milled rice through increasing photosynthetic rate and decreasing N use efficiency. To evaluate the effect of application rate of topdressed N at panicle formation stage on photosynthetic rate of leaf blade and root activity of rice plant, field experiments were conducted. The results obtained were as follows ; 1. When the application rate of topdressed N was increased, the number of grains per unit area, recovery rate of topdressed N by rice plant and protein content of milled rice increased. 2. There was a relationship between application rate of topdressed N and SPAD value, while photosynthetic rate of leaf blade during ripening stage of rice plant was not affected by application rate of topdressed N. 3. No relationship between amount of solution exudated from stem and application rate of topdressed N at the beginning of ripening stage of rice plant was observed. On the other hand, there was a negative relationship between them at the later stage of ripening. 4. When a larger amount of topdressed N was applied, light transmittance became worse.

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