Two inbreds of Zea mays, tolerant to K^+ deficiency and control, were grown in the presence of different concentrations of K^+. Several parameters were compared between the two inbreds and characteristic differences in terms of K^+ utilization were observed. 1. The dry weight of both inbreds was nearly the same in the presence of a sufficient concentration of K^+, but was apparently higher in the tolerant inbred than the control inbred according to the decreasing amount of K^+ supply. 2. Symptoms of K^+ deficiency in the tolerant inbred appeared only with complete absence of K^+, but those in the control inbred could be observed even at a decreased level of K^+ supply. 3. The increased length of the main root and top to root ratio in the control inbred were conspicuously lower than those of the tolerant inbred due to K^+ deficiency. Furthermore, the amout of lateral roots of the cotrol inbred was approximately one-half to one-fourth of that of the tolerant inbred. 4. The capability of K^+ absorption by the roots treated for K^+ deficiency was higher in the tolerant inbred than in the controel inbred. The difference in the capability became larger when assayed with decreasing concentrations of K^+. 5. K^+-dependent H^+ extrusion from roots treated for K^+ deficiency was larger in the tolerant inbred than in the control inbred.

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We measured the amount of microbial biomass and some physicochemical properties of 9 volcanic ash soils and 7 non-volcanic ash soils in Japan and analyzed their relationships. The results obtained are as follows : 1) The amounts of biomass C and N did not significantly differ between the volcanic (58-1504 mgC kg^<-1>, 10-180 mgN kg^<-1>) and non-volcanic ash soils (11-1118 mgC kg^<-1>, 2-124 mgN kg^<-1>). 2) Both in volcanic and non-volcanic ash soils, the amounts of biomass C and N showed significant relationships (r≧0.826^*, n=7) with organic C content, total N content, total humus content, NaOH-extracted humic acid content, NaOH-extracted fulvic acid content and Al_2O_3 content. The relationships between the amounts of biomass C and N and the CEC and phosphate absorption coefficient were significant (r≧0.809^<**>, n=9) only in volcanic ash soils, and the relationship between the amount of biomass and clay content was significant (r≧0.839^*, n=7) in non-volcanic ash soils. The soil characteristics having significant relationships (r≧0.902^<**>, n=9) with the amount of biomass also showed significant relationships (r≧0.827^*, n=7) with fulvic acids, total humus, humic acids or organic C contents. 3) The relationships between the amounts of biomass C and N and several soil characteristics such as organic C, total N, total humus, fulvic acids, humic acid content, CEC, phosphate absorption coefficient and Al_O_3 content can be separated into two groups: volcanic ash soil group and non-volcanic ash soil group.

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A new fertilizer system to improve phosphorus availability was developed using cabbage plant (Brassica oleracea L.) by applying phosphorus before transplanting. When potassium, ammonium or sodium phosphate monobasic solution was applied to cabbage seedlings before transplanting, the weight of the cabbage head was the same as that when using the common fertilizer system. The amount of phosphorus uptake increased when 40% or 20% P was applied before transplanting, especially during the early stage after transplanting. Consequently, 30-60% of the phosphatic fertilizer was reduced, and phosphatic availability was improved 2.5 times. However, no effect was observed when controlled-release fertilizer was applied. This high phosphorus availability was due to high phosphorus absorption resulting in a high growth rate during the early stage, as well as less phosphorus fixation in the soil. However, excess phosphorus often induced salt injury such as chlorosis and leaf burn. So, further studies to overcome injury to the plant are required.

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We investigated the difference in cadmium (Cd) amounts of caryopses among the positions of rachis-branch in an ear of paddy rice. The Cd amounts accumulated in the hulled grains varied among the caryopses in an ear, and the coefficient of variation of these amounts was more than twice as compared to that of grain weights. A negative correlation between the grain weight and Cd content percentage was observed, and the accumulation of Cd in small grains was greater than that in big grains. Cd accumulation in the rice grain was greatest in the caryopses set on the primary rachis-branch in the lower part of the ear. In a single rachis-branch, Cd was greatest in the caryopses set at the second and third positions in the primary or secondary rachis-branch. These results suggest that the variation of Cd accumulation in caryopses in an ear might be due to the difference of Cd accumulation between inferior and superior caryopses.

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We examined the behavior of coated phosphate and potassium in Andosol. Seedlings of Allium fistulosum L. were grown in Andosol applied with a PK fertilizer and coated fertilizer. In coated PK fertilizer, there are cases where the amount of absorbed phosphate to the plant was enhanced without increasing available phosphate in the soil. This suggests that plants would be able to absorb phosphate from the coated fertilizer directly not via available phosphate in the soil. On the other hand, the eluviation of potassium in coated PK fertilizer was clearly suppressed. Coated phosphate and potassium would be valuable for availability through application to Andosol.

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The release rates of Ca, Mg and K from six green manure (clotararia, pigeon pea, sesbania, guinia grass, sorghum and oats) and three composts prepared from poultry manure, cattle feces and sugar-cane leaves were measured. Green manure and composts wrapped in glass-fiber filter paper were placed in Ap horizon of a Dark Red soil and analyzed for Ca, Mg and K after 1, 3, 6 and 12 months. In addition, the chemical forms of Ca, Mg and K in the original organic materials were characterized by successive extraction with water, 1 tool L^<-1> NaCl, 2% acetic acid and 0.6 mol L^<-1>HCl. For all the materials, more than 90% of K and Mg was water soluble and water plus 1 mol L^<-1> NaCl soluble, respectively, whereas the water-soluble fraction was variable for Ca, ranging from 4 to 68%. The release rate followed the order of K>Mg>Ca for all the materials, reflecting the proportion of water-soluble fraction. For three bases, the release rate was higher for the green manure than for the composts. The amount of K released from the materials in the first 1 month was highly correlated with the water-soluble K, giving the regression of y=1.04χ-0.04 (r=0.99^<**>), where χ and y stand for the amounts of water-soluble K and released K, respectively. Similar relations with lower correlation coefficients were found for Mg, y=1.02χ+0.03 (r=0.84^<**>), and Ca, y-0.67χ+0.08 (r=0.78^*).

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The effects of gypsum on the decomposition of rice straw and rice straw manure were examined in comparing with those of hydroxy-Al.1) The dry weight of rice straw, rice straw with gypsum and rice straw with hydroxy-Al at 12 weeks into the humification process were 27, 35 and 56% of initial dry weight, respectively. The C/N ratio of both rice straw and rice straw with gypsum were changed similarly, and after 12 weeks of incubation at 50℃, the C/N ratios of both treatments were about 8. On the other hand, that of rice straw with hydroxy-Al was significantly higher (13 at 12 weeks). 2) The rate of nitrogen mineralization of rice straw manure and rice straw manure with gypsum were almost equal at 35 d of incubation. After 35 d of incubation, however, the mineralization rate of rice straw manure with gypsum was higher than that of rice straw manure. The decomposition ratio of rice straw manure with gypsum treatment was lower than that of rice straw manure. The decomposition ratio of rice straw manure with hydroxy-Al was significantly lower than the ratios of the others. 3) The kinetics of the carbon mineralization process of rice straw manure were studied. The amount of potential decomposable carbon in rice straw manure treated by gypsum was 12% lower than rice straw manure with no treatment, however, the mineralization rate constant was not different between the two. With hydroxy-Al treatment, both the decomposable carbon and the mineralization rate constant were 33 and 62% of the rice straw manure with no treatment, respectively. These results indicate that gypsum and hydroxy-Al have an effect on the control of decomposition of rice straw and rice straw manure. However, the effect of hydroxy-Al was so strong that the nutrient supply from manure becomes much smaller. Therefore, gypsum is a more favorable material to control the decomposition of rice straw manure.

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In order to evaluate the ability of a rice paddy to remove nitrate, and the effects of nitrate on the rice plant, in 1993 we investigated the outcome of nitrate introduced by groundwater irrigation, and the growth and yield of rice in a paddy surrounded by a large area of upland fields. The average nitrate concentration of the irrigation well water was 33.8 mg N L^<-1>, and the total input of nitrate was 444 kg N ha^<-1>. Nitrate concentration in the surface water decreased with distance from the water inlet towards the interior of the rice paddy. Starting 4 d after flooding the paddy, percolating water collected from four test points at a depth of 10-14 cm showed very low nitrate concentrations, an average of 0.01 to 1.17 mg N L^<-1> The nitrate removal rate, which varied according to the concentration in the surface water, in fact reached up to 1 g N m^<-2> d^<-1> with nitrate concentrations of more than 25 mg N L^<-1>. The rice plants did not absorb nitrogen excessively, in spite of the high degree of nitrate loading, and grew normally with no damage such as overluxuriant growth or lodging. Hence, the grain yield was not any lower than the average in the region. Additionally, we found that the soil nitrogen content, of both inorganic and available nitrogen, did not increase during the irrigation period. Therefore, it was suggested that the nitrate removal through percolation was caused neither by absorption by the rice nor by soil adsorption, but mainly by denitrification. The total input of nitrogen including irrigation, fertilizer and rain was 487 kg ha^<-1> The amount of nitrogen loss into the environment was very small, 20 kg N ha^<-1> through percolation. Therefore, the nitrate removal ratio was estimated to be 96%. It is concluded that rice paddies have an exceptionable capacity to remove nitrate, which is significant in controlling the nitrogen cycle in agricultural ecosystems for water quality conservation.

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We determined the annual changes in the gross rates of nitrogen transformations using the ^<15>N-ammonium isotope dilution method for soils where a rice paddy was converted to an upland field. In the converted field, we raised soybean and examined the relationship between growth and yield of soybean and the rates of N transformations. In consequence, the annual changes in the microbial activities of N transformation caused by conversion of the field were revealed. We discussed the environmental factors controlling the changes of N transformations and the effects of N transformations on the growth and yield of soybean. The results obtained were as follows. 1) Both the rates of N mineralization and immobilization decreased in the first year after field conversion. Although the mineralization rate increased after the second year, the immobilization rate continued to decrease year by year. The nitrification rate increased with the passage of time. The decrease in immobilization rate could be attributed to the decrease in moisture content of the soil and to competition for ammonium between heterotrophs and nitriflers. 2) The yield of soybean increased for three consecutive years after field conversion. This increase could be attributed to the increase in the supply of soil nitrogen during the initial and middle stages of the growth of soybean, because an increase in the number of pods and grains per pod resulted in the increased yield. 3) The amount of weeds growing in the converted field increased year by year. The mixing of the weeds at the time of plowing would result in enhancement of the initial growth of soybean, because the weeds mixed into the soil enhance the absorption of N by soybean during the initial growth stage.

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The Kurobokudo samples collected from 12 sites in northeastern Japan were fractionated using S. g. 1.6 Mg m^<-3> and 2.0 Mg m^<-3> sodium polytungstate solutions. Both fractions, less than s. g. 1.6 (<1.6 fraction) and s. g. 1.6 to 2.0 (1.6-2.0 fraction), were observed by light and electron microscopy, and the organic carbon contents of these fractions were determined. Also, the humus composition of the soil samples was analyzed. 1) Charred plant particles were the main component in the <1.6 fraction. The charred plant residues of the 1.6-2.0 fraction occurred in association with mineral colloids. 2) The organic carbon content of the <1.6 fraction tended to increase with the increase of that in the 1.6-2.0 fraction. 3) The proportion of organic carbon in the <1.6 fraction to that of the soil sample ranged from 1.7 to 15.9%, and the proportion of 8 samples within 12 samples was more than 6%. 4) The organic carbon content of the <1.6 fraction was correlated with the total humus content, but was not related to other characteristics of the humus composition. 5) All the humic acids belonged to the A-type with a high degree of humification.

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Laboratory experiments were conducted to evaluate soil physical properties on the elongation of soybean (Glycine max Merr.) root germinated in a seed bed and grown to the soil core. Soil cores having variable soil-water contents and dry bulk densities were prepared for the test of root elongation. Soil mechanical impedance strongly influenced root elongation at the initial stage of root penetration into the core. The elongation rate of a root penetrated into the soil core for 1 d was influenced by both the dry bulk density and soil mechanical impedance. The soil hardness of a volcanic ash top-layered soil was measured to be in the range of 0.01-8.07 N, and there was no difference between the 5 and 10 mm penetration depth measurements. The difference in soil hardness was measured in 5 mm graduations, ascertained using a guide for the measurement. After these experiments measuring soil hardness with the pinpenetrometer, it was shown that this procedure is suitable for evaluating subtle differences in soil unevenness. The pinpenetrometer, which can measure soil hardness in 2 cm-thick layers, is incompatible with Yamanaka's penetrometer.

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Laboratory experiments were conducted to evaluate soil physical properties on the elongation of soybean (Glycine max Merr.) root germinated in a seed bed and grown to the soil core. Soil cores having variable soil-water contents and dry bulk densities were prepared for the test of root elongation. Soil mechanical impedance strongly influenced root elongation at the initial stage of root penetration into the core. The elongation rate of a root penetrated into the soil core for 1 d was influenced by both the bulk density and soil mechanical impedance. A reduction in the air porosity under wet soil also hindered the elongation rate due to insufficient oxygen supply to the root. Dry bulk density influences root elongation through the supply of pore space, and it was the second dominant factor for elongation. As root can easily make its own pore space for elongation with increasing soil-water content, this was the third factor affecting elongation. The role of soil-water to maintain root pressure could not be confirmed from our short-term experiments. It can be concluded that mechanical impedance is the most appropriate expression for root elongation because it includes the effects of soil-water content and bulk density.

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The effect of fertilization method on the occurrence of potato scab was investigated in allophanic Andosols in the Iburi area of Hokkaido, Japan. At the flowering stage, the pH of the soil horizon where the potato tuber grows, was lower significantly in the treatment where ammonium sulfate was supplied in the rows and phosphate and potassium were supplied to all over the surface soil (group A), and in the treatment where all fertilizers were supplied to all over the surface soil (group B) than that in the control treatment where all fertilizers were supplied in the rows. At the flowering stage, the pH was 4.5 in the control group, 4.3 in group A and 4.0 in group B. The occurrence of potato scab decreased both in groups A and B. The scab severity index was 82 in the control group, but 12 in group A and 4 in group B. The aluminum ion concentrations in the water extracts of the soils were between 0.3 and 0.8 mg L^<-1> in soils with a pH lower than 4.5. Potato common scab was suppressed when the aluminum concentration in the water extract was higher than 0.3 mg L^<-1>.

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Investigations were made on the growth and yield of soybean in terms of soil temperature and soil water potential under mulching with coffee residue and polyethylene film. 1) Mulching with coffee residue and polyethylene film markedly decreased weed biomass and increased the growth and pod yield of soybean in contrast to unmulched control soil. 2) After the cultivation of soybean, the soil mulched with coffee residue possessed higher contents of inorganic N and total N than the unmulched control soil and soil mulched with polyethylene film. 3) The minimum temperature was about 3℃ higher in the soil mulched with coffee residue than the unmulched control soil, and about 1℃ higher than the soil mulched with polyethylene film. However, the soil mulched with coffee residue maintained the lowest level of maximum soil temperature when compared to the other treatments. 4) The control soil and soil mulched with polyethylene film exhibited a large lowering of soil water potential during the drying period. However, the water potential in the soil mulched with coffee residue was almost constant throughout this study. 5) The decomposition of soil mulched with coffee residue was slow. Therefore, it is believed that mulching effects, such as weed control, soil temperature and soil water potential, extend the harvesting time of soybean. From these results, it is believed that mulching with coffee residue enhances the growth and pod yield of soybean by increasing the minimum soil temperature and soil water potential.

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