^<15>N tracer experiments in the experimental field of Hokuriku National Agricultural Experiment Station were carried out. the effects of compost and rice straw application on the fate of mineralized soil nitrogen were examined. Seven plots were set up, namely, a non-application plot, a standard rate of compost application (compost 1 ton/10a) and higher rates of compost application (compost 2 and 3 ton/10a) plots, a standard rate of rice straw application (rice straw 0.6 ton /10a) and higher rates of rice straw application (rice straw 1.2 and 1.8 ton/10a) plots. At each time of planting, active tillering, young panicle initiation and booting, nitrogen was applied at the rate 3 g/m^2. The results obtained are summarized as follows: 1) Immobilization, denitrification, and absorption by rice plants of the mineralized soil nitrogen NH_4-H existed at each time. (1) Immobilization: Percentage of immobilization at the time of planting was in the following order: higher rates of rice straw application > standard rate of rice straw application > higher rates of compost application > standard rate of compost application > non-application. The amount at the time of active tillering showed that higher rates of rice straw application was higher than other plots. However, the amount of each plot at the time of young panicle initiation and booting was nearly the same. (2) Denitrification: Percentage of denitrification at the time of planting was in the following order: rice straw 1.8 plot > rice straw 1.2 > rice straw 0.6 > compost application > non-application. However, the amount of each plot at the time of active tillering, young panicle initiation and booting was nearly the same. (3) Plant recoveries: Ratio of absorption by rice plants increased with the advance of plant growth. Effect of compost and rice straw application showed a tendency that the ratio of those at the active tillering time was low by the higher rates of rice straw application plots. 2) Transfer from mineralized soil nitrogen to immobilization, denitrification, and absorption by rice plants. The total amount of nitrogen transferred from mineralized soil nitrogen was 19.4 g in the non-application, 21.0 g in the standard rate of compost, 19.7-21.9g in the higher rate of compost, and 17.7-18.2 g/m^2 in the rice straw plots. The total amount of nitrogen immobilized increased with compost and rice straw application. The total amount of nitrogen immobilized increased with compost and rice straw application. The total amount of nitrogen absorbed by rice plants increased with compost application and decreased with rice straw application. The total amount of nitrogen denitrified decreased with rice straw application.

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Biological control of brown stem rot of adzuki beans, a soil-borne disease caused by Cephalosporium gregatum, through an organic amendment to the seedling rhizosphere was investigated. In the experiments, farmyard manure (FYM), bark compost (BC), and compost made of the diseased stem (CDS) were used. Result were summarized as follows. 1) In a preliminary experiment, each of FYM, BC, and CDS at the rate of 50 t/ha was ploughed into a diseased monocropping plot on light-colored Andosol. These materials depressed the incidence of brown stem rotting and stimulated the plant growth. Among the materials, FYM and CDS retained higher ability of the disease control and of plant growth stimulation. 2) For setting up a feasible technique of organic amendment with a necessary but minimum amount of organic material, a rhizosphere application technique was examined in the following way. Small paper pots, 3cm in diameter and 5cm in length, were packed with any of the diseased soil, a sound soil, and the sound soil mixed with any of FYM, BC, and CDS (1:1 w/w), and then planted with adzuki bean seeds. Then the pots were transferred into a field heavily infected with the pathogen. In the paper pots with organic amendment, the root development was markedly stimulated, and growth of adzuki beans was significantly increased also. 3) When the paper pots with organic amendment was applied, root mycoflora outside the pot became not only higher in diversity, but also higher in similarity to those inside the pot, even at the flowering stage. Diversity of root mycoflora as expressed by Brillouin's index was negatively correlated with the incidence of disease, and positively with the root weight. 4) The rhizosphere application technique was also examined in farmers' lightly infected fields on three types of soil. The results demonstrated a significant depression of disease incidence, resulting in stimulation of plant growth and yields. The higher the index of diversity of root mycoflora, the less the incidence of disease and the greater the root weight. 5) Actinomycetes and bacteria antagonistic to the pathogen were isolated from the organic materials-the most abundant antagonists being from CDS. This result indicates that the compost made of diseased crop residues could be the biocontrol agent. 6) An amount of the organic materials used for the rhizosphere application in the experiment was as small as 1.4 t/10a.

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The abnormal hardening of topsoil after puddling in the rotational paddy fields was discussed in respect to the finding in some field surveys and a questionnaire to farmers. The outline of this study is summarized as follows: The topsoils of rotational paddy fields hardened after puddling regardless of soil type when compared with continuous cropping fields. The actual damage to plant growth, however, occurred only in the soil texture coarser than loan. The shrinkage volume with drying, the mean weight diameter of aggregates, the sedimentation volume, the specific surface area, the liquid limit, the plastic limit and the total content of carbon decreased in the topsoil of rotational paddy fields. the negative correlation was established between these values and the hardness of topsoils. The hardening of puddled soil in rotational paddy fields should be caused by the destruction of aggregates with the decrease of organic materials and the drying after drainage. It was supposed that the single grains facilitate close filling, which results in hard topsoils. The physical indicators and the content of organic materials in the rotational paddy fields were not recovered at least three years after converting again to paddy fields.

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The decomposition process of shochu distillers wastes applied into two kinds of soil-Kanagawa soil (silty clay loan) and Kagoshima soil (loam)-was carried out at 25℃ in the dark by keeping the moisture content at 55-60% of the maximum waster holding capacity of the soils. Gel chromatography of water extract of the soil-waste mixture during incubation was monitored at UV 280 nm. Values of pH, EC, and concentration of NH_4^+-N and NO_x^--N were measured, and the seedling test of komatsuna (Brassica compestris L. var. rapiferafroug) for 72 h was carried out to investigate the inhibitory effect. The experimental results were as follows: 1) By the gel chromatography, the wastes were judged to be stabilized in soil in 28 days for Kanagawa soil and 14 days for Kagoshima soil. 2) No significant inhibitory effect of the waste in soil was observed for the seedling test after 3 days incubation from the start of the experiment. The growth stimulation effect on the stabilized soil was observed in our experiment and the practically waster-treated soil in Kagoshima. 3) The increase of maximum water holding capacity, cation exchange capacity, nitrifying capacity, and concentration of inorganic nitrogen in long-term treated oil was significant compared with non-treated soil. It is concluded that the land application of the waste with respect to its treatment can be recommended from the soil improvement and economical points of view.

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A series of experiments were conducted to study the relationships of the water stress tolerance in warm season forages to their root hydraulic conductivities, root pressures, and exudation rates. Chloris gayana and Coix lacryma-jobi were used as test plants of which the former species was classified as one of the most tolerable and the latter, the weakest, to the water stress. Both plants were grown with pot culture adjusted to pF 1.7-2.0 and pF 2.8-3.2 of soil moisture. And then tritium (^3H) labelled water was injected to their rhizospheres and exudations from the cut surfaces of stem base were collected to determine radioactivity of ^3H. The dry weight of shoots and roots in both plants reduced under the water stress condition particularly in C. lacryma-jobi. The total root length and surface area of roots in C. gayana were 1.5-2.0 times as large as those in C. lacryma-jobi under the water stress condition. ^3H contents in the exudation of both plants watered well were higher than those obtained in the water stressed. In the exudation of C. gayana, ^3H was obviously detected about 2 h after injection of ^3H_2O and increased with time under the water stress condition, while ^3H in exudation of C. lacryma-jobi delayed markedly and was about one-sixth that of C. gayama. The decreases of ^3H in exudation found under the water stress was due to decrease of the exudation rates and of ^3H-specific activities in xylem sap. Thus, C. gayana can transport water more effectively, compared with C. lacryma-jobi, from root to shoot under the water stress condition. the hydraulic conductivities of the tested plants were appreciably lowered by the water stress and estimated as 431 mg H_2O/g root/h/bar for C. gayama and one third of C. gayana for C. lacryma-jobi under the water stress of -1.55 bar of the cultural solution in which the water potential was adjusted by additions of polyethylene glycol 6000. The root pressures of C. gayana and C. lacryma-jobi were estimated by using the cultural solution of various water potentials as 3.11 and 2.35 bar, respectively. From these results it is assumed that the tolerance of plants to the water stress is dependent on the root hydraulic conductivity and the root pressure which are main factors in the transfer of water from roots to shoots under the water stress condition as well as root developing abilities.

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The present paper attempts to estimate the contribution made by diffusion dispersion, and mass flow to the NO_3-N supply to plant roots in a field condition, and the minimum NO_3-N concentration of the soil solution for the maximum growth of corn plants. We employed a single root model, and the results obtained are summarized as follows: 1. The transport of NO_3-N to the roots was mainly achieved by mass flow in the high level of soil NO_3-N content while in the low level of soil NO_3-N it was achieved by diffusion and dispersion. 2. The contribution of diffusion and distribution to the NO_3-N transport was closely related to the root density. Dispersion contributed most to the NO_3-N transport in the low root density while diffusion made the biggest contribution to the high root density in clay soil. 3. In sand soil which was low in initial moisture content (pF2) compared with clay soil, dispersion was the main mechanism of NO_3-N transport at the same level as the NO_3-N content of clay soil. 4. In a field condition, the minimum NO_3-N concentration of the soil solution for plant growth may be determined by such factors as the water and nitrogen requirement of plants, the NO_3-N transport rate to the roots, and by the soil texture, etc. In addition to these factors, it was found that the minimum concentration is governed by the root density. It also seemed probable that the minimum NO_3-N concentration for plant growth is the lowest NO_3-N concentration of the soil solution which does not make the NO_3-N concentration on the root surface zero.

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In the paddy field where the chemical properties of the soil were affected by the continuous application of swine urine, the physical properties, especially the bearing capacity and soil structure, were examined as indications of farm machinery trafficability. The bearing capacity of the soil supplied with swine urine continuously was much lower than that of the soil supplied with chemical fertilizers and it was impossible to drive a tractor in the former field 35 days after surface drainage. The capillary pore content in lower suction range, plasticity index and sedimentation volume of the topsoil increased with continuous application of swine urine. In the ill-drained paddy field, it is considered that continuous application of swine urine worsens its wet feature, lowers its bearing capacity, leads to formation of weak soil structure, and lowers the farm machinery trafficability.

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The purpose of this investigation is to clarify the effect of farmyard manure (FYM) on the distribution of nodule formation and nitrogen-fixing activity in the root systems of soybeans. Soybeans were grown in plastic faced-root boxed supplied with FYM of different quality and size, by two methods. The results obtained were as follows. 1) Nodule formation and nitrogen fixation of soybean was more markedly decreased by whole layer application that by row application of FYM with high available nutrients: however, there were few differences in distribution patterns on nodule formation and nitrogen-fixing activity in the root systems. 2) The application of washed FYM with low available nutrients (W-FYM) resulted in the increase of nodule formation and nitrogen fixation and the enlargement of their distribution in root systems, irrespective of application methods. Moreover, the effectiveness was more strongly recognized in the whole layer application than in the row application 3) Soybean root penetrated into W-FYM placed in soil as row application while it almost did not penetrate into FYM. 4) the improvement of nodule formation and nitrogen fixation, and the enlargement of their distribution patterns were obtained by the application of granular FYM of large size (10-20 mm in diameter) compared with that of granular FYM of small size (2-4 mm in diameter). 5) It became apparent from this root box experiment that nodule formation, nitrogen fixation, and their distribution patterns in soybean root systems were remarkably influenced by the quality, size, and application method of FYM.

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1)Amounts of dry matter, sugar, starch, nitrogen, cellulose, hemicellulose, lignin, free amino acids and amides, protein-amino acids, allantoin, allantoic acid in the leaves, stems, pods, seeds, nodules, and roots of soybean plants were determined at the maximum leaf-and-stem weight stage and at harvest. 2) During the course of seed filling, the amount of starch decreased gradually, that of sugar increased considerably, and those of cellulose, hemicellulose, and lignin were kept almost constant in the leaves and stems. From these facts it is appropriate to consider that only a small amount of storage carbohydrates in the leaf-and-stem is used for respiration or retanslocated to the seeds. 3) Out of the total amount of nitrogen in the plant at harvest, 64% was absorbed till the maximum leaf-and-stem weight stage and the last was absorbed or fixed after that growth stage. Out of the total amount of nitrogen in the seeds at harvest, 33% was considered to be retranslocated from the leaf-and-stem and the rest was absorbed or fixed during ripening. 4) Soluble-N occupied 50% of the total-N in the stems and pods, but was much lower in other organs. Allantoin and allantoic acids-N occupied roughly 10% and 2% of total-N in the stems and pods, pespectively, but was negligible in other organs. Thus, it appears that allantoin is translocated from the root nodules to the stems and pods, and then decomposed in these organs before the nitrogen in these compounds is incorporated into the protein in seeds. 5) Major free amino acids and amides were aspartic acid, glutamic acid, asparagine, and glutamine in all organs. Proportions of various amino acids varied with age and by organs. However, as asparagine occupied more than 50% of the total amount of free amino acids in the stems and pods, asparagine is considered to be the major nitrogen-translocations form, 6) The amino acids composition was similar among proteins in various organs, and also in an organ with different ages. However, the amino acid composition of proteins in an organ differed from that of free amino acids in the organ. These facts suggest that during the course of translocation of nitrogen from the leaves to the seeds, complicated reorganizations of amino acids take place in the leaves and again in the seeds.

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