This study was undertaken to clarify the effects of nitrogen application rate in basal to top dressing at panicle formation stage and planting density on the relative development of sink (number of spikelets per m^2) and source (Leaf Area Index [LAI]at heading time), that is, sink/source ratio. We also discussed the relationship between the sink/source ratio and the dry matter production or yielding ability for the establishment of a stable high-yielding cultural method, using young seedlings, in the southern district of Japan. The results are summarized as follows : 1) Sink/source ratio changed mainly depending o the amount of source, not on that of sink. As LAI was increased in proportion to planting density, the higher the planing density was, the lower was the sink/source ratio was less, and it was little changed among plots applied rate in basal dressing on the sink/source ratio was less, and it was little changed among plots applied 20-100% nitrogen in basal dressing, except the non-basal nitrogen application plot, in which sink/source ratio was increased because of less development of leaf area. Though sink/source ratio of the plots bearing more than 3.5 million spikelets per m^2 was about 50-80 (spikelets/dm^2 leaf area), it was noteworthy that the sink/source ratio did not decrease according to increase of the sink. 2) The effect of planting density on the yield was markedly greater than that of nitrogen application rate in basal dressing. With increasing the planting density, the higher brown rice yield obtained was due to both superior percentage of ripened grain and 1,000 grain weight. 3) The sink/source ratio showed significant negative correlation with the top dry weight at heading time, but not any significant correlations with the amount of absorbed nitrogen until then or dry matter production during the grain-filling period. Brown rice yield level in the plots with high sink/source ratio, viz., non-application of basal nitrogen or sparse density, was considered to be lower than that in the plots with lower sink/source ratio at the same sink level, because of the inferior percentage of ripened grain through the less amount of reserved carbohydrate in leaf sheath and culm per unit sink (=per spikelet) at heading time.

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We conducted water culture experiments to elucidate the mechanisms of plant stress induced by excess supply of NH_4-N and NO_3-N using tomato and wheat plants. The application of NH_4-N at levels of 40, 200, 1,000 and 2,000 ppm to the culture medium resulted in the growth retardation compared with the plants with 200 ppm NO_3-N and at high NH_4-N levels necrosis or chlorosis appeared on the leaves. The ammonium concentration in leaves increased along with increase of medium NH_4-N. The application of NO_3-N at 1,000 and 2,000 ppm to tomato plants and at 2,000 ppm to wheat plants retarded the plant growth as compared with the plants grown in 200 ppm NO_3-N, but no visible injury appeared on the leaves. High medium NO_3-N caused marked decrease of nitrate reductase activity in tomato leaves but small effect on the activity of wheat leaves. The effect of high medium NO_3-N on nitrite reductase activity was small, and nitrite accumulation was negligible in all treatment with NO_3-N. However, amino acids accumulated to large extents in both plants with high medium NO_3-N. Treatment with high NO_3-N or NaCl in culture medium resulted in accumulation of amino acids, particularly glutamic acid, glutamine, alanine, glycine and proline. The extents of growth retardation and leaf amino acid accumulation were larger in NaNo_3-treated plants than NaCl-treated plants if compared at the same electric conductivities in medium. The growth retardation was closely related with stomatal resistance. It is concluded that NH_4-N stress is caused by large ammonium accumulation in plant tissues, and that NO_3-N stress causes the growth retardation partly due to the disturbance of plant nitrogen metabolism and also to the decrease of stomatal aperture.

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The role of subsoil on nitrogen uptake by rice plants was investigated by field experiments in Hachirogata reclaimed paddy fields. Also, the fitness of models for predicting nitrogen mineralization of plow layer and subsoil to the nitrogen uptake by rice plants was investigated. The results obtained were as follows : 1) Amount of nutrient uptake by rice plants form subsoil was large in rotated paddy fields. 2) At the subsoil in rotated paddy fields, progress of soil reduction was slower and amount of mineralized nitrogen was more than in continuously rice cultivated paddy fields. 3) Amount of nitrogen uptake by rice plants form soil at harvest time was 8.5 g/m^2 in continuously rice cultivated paddy fields and 15.8 g/m^2 in rotated paddy fields. In continuously rice cultivated paddy fields, 20% of nitrogen uptake was absorbed from subsoil and 65% in rotated paddy fields. 4) The process of nitrogen mineralization of plow layer and subsoil and 65% in rotated paddy fields. 4) The process of nitrogen mineralization of plow layer and subsoil was fitted to a single exponential model in continuously rice cultivated paddy fields and rotated paddy fields. 5) After young panicle formation stage, the amount of nitrogen uptake by rice plants in rotated paddy fields was more than the estimation of soil nitrogen mineralization of plow layer and was fitted to the sum of nitrogen mineralization from plow layer and subsoil. It is concluded that the amount of nitrogen uptake by rice plants in rotated paddy field can be enhanced by the nitrogen uptake from subsoil through the penetration of roots into the subsoil.

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1)Although morphologically the truss exserts at the end of the main stem, the main stem combined with the sympodial branch be conventionally considered as the main axis, because the position of the node from which the truss exserts is not fixed under various growing conditions, and also the leaf weight and the leafing interval do not change the main stem and the sympodial branch. 2) Growth of leaves is most active at the 10th node, and that of branches are vigor at the 3rd to 6th, 11th and 16th nodes. 3) Growth of roots and tubers is most active at the 3rd and 4th nodes counted from the ground level. the tubers of the primary 1st stolon grow actively, but those of the lateral 1st, primary 2nd, and lateral 2nd stolons contribute to the tuber yield only slightly. 4) The growth of potato plant could be divided into three phases. Phase I : The shoot weight increases, stolons differentiate and elongate, and then the tip of the stolons starts to swell. Phase II : The weights of the shoot and the tubers increase, simultaneously. The leafing interval becomes longer and the senescence of leaves starts from the lower ones, and then leafing and lateral stolon formation stop. Phase III : The weight of shoot decreases and that of tubers increases. The speed of leaf senescence increases, and weak stolons and tubers abort.

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Grasses have been found to endure iron-deficiency by excreting form their roots mugineic acids which are able to dissolve ferric compounds by forming Fe(III)-complexes. However, mugineic acids were suspected to be rather quickly decomposed by soil microorganisms. The means that mugineic acid-decomposing microorganisms, if present, will mitigate the beneficial effect of the mugineic acids. In addition, the relation between excretion of mugineic acids and mugineic acid-decomposing microorganisms is considered to be a simple model of the relation between plant roots and their rhizospheric microorganisms in the water-cultured iron-deficient barley. Microflora both in the cultural solution and on the root surface appeared to be fairly simple and composed of bacteria. Six strains of mugineic acid-decomposing bacterium was isolated from the barley roots. On the contrary, no mugineic acid-decomposing bacterium was isolated from the cultural solution. This result suggests that the mugineic acid-decomposing bacteria are liable to be adsorbed on the surface of roots. One strain of the bacteria, which could quickly decompose mugineic acid, was judged to belong to Pseudomonas, though no known species were identical with this strain.

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Fractional factorial experiment using 8 lysimeters was applied to compare the effects of four operational factors in rice culture on the phosphorus outflow and balance (input by irrigation-outflow). Four factors and two levels allocated to each factor are as follows : irrigation flow rate (10 and 20 mm/day), nitrogen concentration in irrigation water (+0 and +20 mg/l), phosphorus concentration (+0.0 and +2.0 mg/l), soil condition (fertilized in the past three years and not fertilized before). The lysimeters had little volume of percolated flow. The irrigation period was divided into 4 sub-periods by their characteristics observed in the factorial effects on phosphorus outflow. Period I : high flow rate mainly had a positive effect. Period II : high P concentration increased outflow significantly. Period III : any factorial effects were not significant. Period IV : high P concentration and high flow rate increased the outflow. In the no-irrigation period, phosphorus outflow is free from all factorial effects. From the viewpoint of effects on phosphorus balance (removal), Period I : high P concentration increased the balance. Period II : high P concentration had a positive effect. Period III and Period IV : high P concentration and high flow rate increased balance significantly. No factors which control input of P made the crop increase significantly. The condition which promote the balance contradicted the conditions for decreasing outflow in many periods.

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Landsat Thematic Mapper (TM) data, collected in May 1984 and 1985, were used to estimate and map the soil organic matter contents. The organic matter contents of 30 samples of surface soil, plowing in the depth of 25 cm, were used for linear regression analysis with TM spectral data. Band 3 (630-690 nm) could be used effectively for estimating the soil organic matter contents. Therefore, the next equation was obtained and used for mapping the organic matter contents of upland soils : log Y=1.6112-0.0120 X, where Y is soil organic matter contents and X is computer compatible tape count of band 3 in 1985.

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Landsat Thematic Mapper (TM) data were examined for use in the mapping of soil organic matter content of submerged paddy. Seventy-five surface soil samples from Kuriyama-area in central Hokkaido were obtained for organic matter analysis. The analytical data were used for multiple linear regression of the TM spectral data collected in June 1987. It was found that the set of bands TM1 (450-520 nm) and TM3 (630-690 nm) could be used very effectively to estimate and map surface soil organic matter content under submerged condition.

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The varietal difference in salinity tolerance of soybeans was examined by making a comparison with the relative growth as against control of three organs such as leaves, stem, and root grown in culture solution supplied with 80 mM NaCl. Moreover, the mechanisms of growth suppression of soybeans by a high concentration of NaCl. Moreover, the mechanisms of growth suppression of soybeans by a high concentration of NaCl examined by means of the detachment of leaves and roots, and the equation of osmotic pressure in culture solution. The results obtained are summarized as follows : 1) The varietal difference in salinity tolerance (salinized NaCl) for soybean were mainly due to Na and/or Cl injury rather than to the increase of osmotic pressure in the culture solution. 2) Tolerant varieties showed higher concentrations of Na or Cl ion in leaf blades or stem than did susceptible varieties. 3) To determine the susceptibility or tolerance to salinity, it was better to use the Na or Cl concentration in the stem than in leaf blades, since leaf blades showed a difference in susceptibility to Na concentration among varieties. 4) Sodium or Cl concentration in the stem decreased with the increase of the excluding power of both ions. 5) Varieties with high Na-excluding power had generally higher Na concentration in the root than did low Na-excluding ones when they were grown in culture solution added with NaCl (80 mM) for a short term (2 days).

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Suweon 258, Akenohoshi, Saikai 180, and Saikai 183 of Japonica-Indica crossbreds, and Tsukushihomare of Japonica rice cultivars were planted at the experimental field of Kyushu National Agricultural Experiment Station. The solution containing tracer NH_4-^<15>N at a small amount and high atom % (0.3 g/cm^2, 99.7 atom % ^<15>N) was randomly injected with a long thin needle into the plow layer of the ^<15>N experimental plot encircled with an iron frame of 30×15 cm^2. Twenty-four hours after the injection, rice plants were taken out and divided into root and shoot. From these determinations of ^<15>N atom %, the activity and vitality of the rice root tissue were investigated. The results obtained are summarized as follows : 1) There was an adequate correlation between the rate of ^<15>N absorption by rice plant and ^<15>N atom % excess of the root tissue. From this result, it was considered that ^<15>N atom % of the root tissue was a measure of the activity of root tissue when the vitality of root tissue was defined by the rate of nitrogen absorbed. 2) A large difference was recognized in the atom % excess of ^<15>N in the root tissue among these cultivars at each stage of the ripening period. It weakened with time. The amount in Tsukushihomare was the highest. The amount in Suweon 258 was the same as that in Tsukushihomare from heading to milky stage. But it was lower than the former from the dough stage. The amount in Akenohoshi was the same as that in Suweon 258. The amount in Saikai 180 and Saikai 183 were lower than that in Akenohoshi. 3) The vitality of root tissue at the milky stage was considered to be Suweon 258 = Tsukushihomare ≫ Saikai 180 ≒ Saikai 183 ≒ Akenohoshi. However, the amount at the dough stage was Tsukushihomare ≫ Suweon 258 ≒ Saikai 180 ≒ Akenohoshi.

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