1) The present report deals with the varietal difference on the elongation of the subcrown internode among the representative varieties of barley and wheat in Japan. 2) Seedlings were grown in seeding boxes in which seeds were placed at 3 cm and 6 cm depth under the soil surface. The measurement of the length of the subcrown internode was performed at the stage when the position of the crown had been fixed. 3) All varieties are able to be classified into five classes with respect to the length of the subcrown internode. 4) It is clear that there exists a varietal difference as well as a group difference about the length of the sbcrown internode, by which the position of the crown is determined. 5) Correlation were scarcely found between the other characteristics of a variety, especially cold resistance about which the other workers found it, and the position of the crown. 6) It was discussed that the elongation of the subcrown internode is of much significance on barley and wheat cultures. Further, it was asserted that the method of selection of varieties suited for barley and wheat cultures using modern machines, e. g. drill seeder, should be studied from the point of view above mentioned.

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It was made an attempt to know the safe and effective method of utilizing herbicide CAT in barley and wheat cultivations. 1.) The pot tests were carried out to investigate the circumstances of movement of t he chemical under various conditions combining several kinds of soil and amounts of rainfall, where the seedlings of rape and wheat were used as test plants. It was made clear that the chemical moved into the soil 3 cm depth from the surface, under the condition which had 20 mm rainfall on Nagano loam with a little water capacity and humus content. Some matters that demand special attention for use of the chemical were pointed out from this fact. 2) Differences were found on the germination phases in Alopecurus aequalis var. amurensis between the plants grown on plowed and non-plowed paddy fields. On the plowed paddy fields, plants can emerge easily from the deep parts under the ground. As it causes the growing of numerous number of weeds on the plowed paddy fields, othet suitable means togethet with the chemical should be adopted to weed control in such case. 3) The interrelation between the growing stages of wheat or Alopecurus aequalis var. amurensis and the chemical injuries was investigated. The chemical injury is raised in an early stage when the plants have not attained the leaf number of 2.5. Therefore, the attention should be paid for the growing stage when the chemical is used.

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The author had engaged in research work of rice in Ceylon as a Colombo plan expert in 1961. The results of main experiments conducted by him are summarized as follows. 1. Pot experiment on nitrogen split application (table 1) Growth of rice was divided into five stages and nitrogen was applied as shown in table 1. Compared with nitrogen supply at all growth stages, number of spikelets was most decreased by nitrogen deficit at tillering stage and both number of spikelets and percentage of ripened grains were markedly decreased by that at primordia initiation stage. Consequently grain weight was most decreased in the latter. In case of nitrogen supply at one growth stage, an inverse relation to the above was observed, that is, increase of grain weight was brought about by nitrogen supply at primordia initiation stage. When nitrogen was top-dressed at two stages, the effect on grain weight was the highest in nitrogen supply at primordia initiation stage and reduction division stage. 2. Pot experiment on drainage and percolation of water (table 2 and 3) High rot activity, caused by suppression of soil reduction, and poor tillering were observed in drainage and percolation plot. However, grain weight was not affected by suppression of tillering. Percolation was characterized by high percentage of ripened grains. Re-use of percolated water showed less value of each yield component than no re-use of one. 3. Field experiment on drainage and ridging (table 4) For the purpose of suppressing soil reduction in paddy land of Low-country, drainage and ridging were examined. Drainage showed high yield in both Yala and Maha season. However clear effect was not observed in ridging. 4. Field experiment on cultural improvement in Up-country (table 5) Cultural technics in cold district of Japan were applied, because poor yield in Up-country was assumed to be caused by low air and water temperature. Grain yield was increased under low fertilizer level by using upland seedling, but it was not increased under high fertilizer level. Increased application of P₂O₅ and K₂O showed clear response, but effect of compost on yield was not observed. 5. Field experiment on hill arrangement (table 6 and fig. 1) Hill arrangement was varied in series from square to rectangle under the same density by changing distance between rows and between hills. Grain yield was the highest in medium rectangular arrangement (10"×6") in both H-4 and Murungakayan 302 under standard fertilizer level. Under low fertilizer level, howevr, yield was not so different in accordance with hill arrangement.

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The isolated methods as reported previously, were used on Chiba No. 45 (runner type), and various nutrient solutions were added daily to acid- washed sand of the fruiting zone throughout the experiment. 1. Under the conditions of this experiment, fruit development was prevented at the early stage of its development by deficiencies of every element studied. However, production of unfilled fruit was siginificantly increased only on the plants which received the distilled water or minus calcium solution in the fruiting zone. Therefore, it seems that the formation of unfilled fruit result from deficiency of calcium in the fruiting zone, and that the formation of seed is scarcely effected by all the elements except calcium. 2. The analyses at harvest time showed that calcium deficiency had the greatest effect on the contents of HCl soluble calcium in shell and in seed, reducing them from 0.24 and 0.06 to 0.05 and 0.03 percentages respectively. But any element except calcium which was reduced to low content in shell, had scarcely any effect on its content in seed. Magnesium deficiency increased percentage values for alcohol soluble and acetic acid soluble calcium or alcohol soluble potassium in shell. The same tendencies were recognized in the cases both of calcium deficiency and potassium content and of potassium deficiency and magnesium content. Calcium deficiency also had the greatest effect on soluble-N and NO₃-N content in shell. The content of non-reducing sugar in shell was remarkably increased in unfilled fruit with abnormal seed. Also the content of starch in abnormal seed was markedly increased. 3. Behaviour of magnesium content, especially acetic acid soluble, during the fruit development made a sharp distinction between calcium deficiency and other deficiencies in this experiment. The same tendency was more clearly found on behaviour of potassium content. Increasing of HCl soluble calcium was hardly observed in the case of calcium deficiency. Nitrogen content, especially NO₃-N, in shell of calcium deficiency showed a differential tendency during the fruit development. In case of deficiencies of every element studied, there was little difference between the decreasing tendencies of carbohydrate and phosphorus content.

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With the plants of runner type (Chiba No. 45 and No. 74), various nutrient treatments were held on acid-washed sand of the fruiting zone throughout the experiment. Flactional analyses of calcium and organic acid were carried out in the pods of each treatment, namely the samples were extracted by 66 % alcohol, 2 % acetic acid and 1 N hydrochloric acid in the case of calcium, and by distilled water and 1 N hydrochloric acid in the case of organic acid. And constituent organic acids were determinated by paper chromatographic methods. 1. Production of unfilled fruit remarkably increased in the plants which received distilled water, minus calcium, plus nitrogen, plus phosphorus, plus potassium and p1us magnesium. In both cases of shell and seed, content of 1 N HCl soluble calcium made a sharp distinction between the above treatments and other nutrient treatments such as complete, minus nitrogen, minus phosphorus, minus potassium, minus magnesium and plus calcium during the peanut development. But in young fruit, the content of calcium by fractional analysis was almost equal irrespective of the treatments of complete, distilled water and minus calcium. 2. The content of free acid (H₂O soluble acid) lessened considerably during fruit development in all treatments holding calcium element. This decrease in acid content was due chiefly to the decrease in contents of free citric and malonic acid. However, the content of free acid in all treatments with-holding calcium such as plus potassium, remained nearly unchanged in shell, and increased in abnormal seed during the season. This increase in acid content of the seed was mainly caused by the increase in content of malonic acid. The content of combined acid (HCl soluble acid) increassed parallel with the content of HCl soluble calcium in shell. And this increased amount was due chiefly to the increase in the content of oxalic acid, so that, it can be conjectured that calcium absorbed from fruiting zone combines with oxalic acid in shell during the maturity. In fact, there were not observed the existence of oxalic acid and the increasing amount of HCl soluble calcium in any treatment of calcium deficiency. But the similar relation was not clear among seeds in all treatments.

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In a previous part we had already reported that the whole cycle of sugar beet plant sown in summer in the warmer districts of Japan would be distinguished into four different and successive stages. However, such growing behavior would be fairly varied with environmental and cultural factors; especially, it is a wellkown fact that nutritional state is easy to effect upon the root yield and its chemical quality of sugar root root. Here, we carried out this experiment to know how nitrogen fertilizer effects to the growing behavior. The variety used was D0-nyu No. 2 sown on August 16, and three nitrogen levels were set up as seen in Table 1. The results can be summarized as follows: The growth of top part is more vigorous in order of high, intermediate, and low nitrogen levels (fig. 1, 2), but the development of storing root is hot always the more vigorous under the higher levels, i. e. there is no difference between high and intermediate (fig. 3). These results show us that too much growth of top does not contribute to development of storing root. The turning times from rapid growth stage to root ripening one are clearly retarded under higher level, and winter-kill of leaves is less, but the initial times of regrowth under three levels is nearly simultaneous, perhaps inducing by rising of air temperature over about 10°C (fig. 1, 2). Sugar content in root is pretty higher under high level than under low one, though there is no principal difference in varing trend (fig. 5). On the other hand, we could find an noticeable phenomenon about variation of sugar purity, that is, the purity under high level drops temporarily for a while after beginning of regrowth, after which it is rising again, and it is also closely associated with reverse variation of root nitrogen compositions (fig. 6). This phenomenon is probably due to accumulation of excessive nitrogen taken up out of soil into the storing roots. On the seasonal variation of reducing sugar, raffinose, ash and unsoluble solid in root there is no principal difference with nitrogen levels. From the results described above, the growing behaviors under higher and lower nitrogen levels could be illustrated schematically as shown in fig, 10.

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From experiments until now it has been known that when the sugar beet plant is cultivated in the warmer districts of Japan, summer-sown type is most ideal from both points of root yield and its chemical quality if in a suitable environment. However, the climate during August is apt to bring severe damages to seed germination and to seedling growth by too high temperature and by too little or much rainfall. Accordingly, it is now thinking that it is rather better to sow after August for avoiding these damages. Here, we traced the growing behavior of sugar beet plant sown in September, and discussed comparing it to the plant sown in August. The varieties used were two, Do-nyu No 2 and KW-AA, and both were sown on September 9 and 27. The summarized results are as follows: Both the top growth and root development up to December are very poor and winter-kill of leaves is very little, in comparison of summer sown plants. However, the plant regrowth from early March gets very rapid (fig. 1.2). On the other hand, the root development in fall-sown plants till late December is extraordinarily poor, accordingly, the main part of stored root must be expected in development during spring (fig. 2, tab. 4). R·T ratio is in a trend of decreasing and after then increasing, having a bottom in late March, and is always higher than in summer-sown plants throughout the life cycle (fig. 3). This shows us that the producing efficiency of aerial part to storing root is fairly lower in fall- sown plants. Numbers of brix and pol in root keep until late February and after then decrease rapidly as in summer-sown plants, however, decreasing rate is relatively more than in summer-sown plants. Accordingly, when a time of harvest would be decided by a certain sugar per cent, it in fall-sown plants, though having young age, is not always prolonged later than in summer-sown plants. It is around late April or early May (table 5). Conclusively speaking from the results above, the fall-sown sugar beet cultivation would be much useful in regions with higher air temperature in winter and with conditions, in which the decrease of sugar content in root during spring is relatively less.

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The non-ripened grains contain two kinds of grains, viz., non-fertilized grains and imperfectly ripened grains (which have abortive kernles), and a method for predicting non-fertilized grains just after anthesis has already been reported by the same authors (Vol. 28, No. 4), so they have studied here the occurrence of abortive kernels which are determined at the early ripening stage and a method for predicting them. The results may be summarized as follows. 1. As a result of having studied the ripening process by classifying grains with specific gravity, the authors have found that there are two peaks in the distribution of specific gravity of grains, viz., the one is lower than 0.84 and the other is higher than 1.04 specific gravity, and very few grains distribute between the two peaks, and also the number of grains which are lower than 0.84 specific gravity is quite influential in determining the percentage of ripened grains. 2. Having classified the grains lower than 0.84 specific gravity into 7 classes according to the size of their caryopses and traced up their ripening processes, the authors have found that the grains belonging to the classes I to IV (which have small caryopses) can be discriminated from the other grains as abortive kernels which occur at the early ripening stage (cf. Fig. 2). 3. Abortive kernels begin to occur at the time at which the starch-content in culms attains its minimum, and, according to the criterion established by the authors, the time can also be expressed as 10 in the ripening grade of the panicle or the hill. (cf. Vol. 29, No. 4). 4. The percentage of abortive kernels which cccur at the early ripening stage on the central primary rachis -branch, which is located at the center on the axis of a panicle, can always represent the percentage of the whole panicle. 5. From the results obtained in the present experiment it has been made clear that the abortive kernels which occur at the early ripening stage can be discriminated from those which occur at the late ripening stage and the former can easily be predicted much earlier than the latter can be done.

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For maximizing the yield of rice it is quite necessary to obtain high percentages of fully ripened grains under the condition in which too many spikelets per unit area have been borne. Conducting many experiments for long years, Matsushima, one of the authors, realized that it could by no means be achieved without using productive soil, but recently he noticed an idea that it might be achieved not by using any productive soil, but by controlling growth habit (i. e., shortening the lengths of upper 3 or 4 leaf-blades and those of inter-nodes for avoiding the mutual shading of individual leaves) and by increasing the rate of carbon assimilation per unit leaf-area after heading. The authors, therefore, tried to maximize the yield by growing rice plants by water-culture under community conditions, and compared them with those grown in ordinary paddy fields in which a large amout of compost was applied. (By using water-culture, one can easily control the growth habit of rice plants at any growth stage by increasing or decreasing the concentration of nitrogen in the solution.) As a result of it, the rice plants grown by water-culture yielded the amount of 101.6 kg and 77.2 kg of kernels (brown rice) per are, while those grown in paddy fields produced only 57.6 kg at the most. In the present experiment a main control of growth habit was done by decreasing the nitrogen concentration in the solution or taking off nitrogen from the solution during the period from 41 days to 20 days before heading, making the plants short in the lengths of upper 3 or 4 leaf-blades and those of inter-nodes and also thick in the thickness of leaf-blades. On the basis of these facts, the authors concluded the meaning of the application of organic fertilizer as follows; i. e., under the condition of no harmful effects caused by decomposing organic matters in soil being found, organic fertilizers (1) supply the necessary and sufficient amount of all kinds of nutrient elements to the plants through their whole lives, and (2) act as a "buffer" not to supply nitrogen to an excess during the period in which the lengths of upper 3 or 4 leaf-blades and those of inter-nodes are determined.

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Subjecting the rice plants to nitrogen-depletion treatments, nitrogen top-dressing treatments and root-pruning treatments at different growth stages, the authors examined the effects of the treatments on the lengths of leaf-blade, sheath and inter-node born on each node by comparing the lengths with those of non-treatments, succeeded in establishing a method for controlling their lengths. 1. Increasing the supply of nitrogen is quite effective for lengthening each leaf-blade, sheath and inter-node, while decreasing the supply is most important for shortening them. 2. There is found a definite e synchronous growth among leaf-blades, sheaths and inter-nodes, i. e., taking B₁, B₂, B₃, B₄………as the 1st (upper-most), 2nd 3rd and 4th leaf-blade from above and taking S₁, S₂, S₃, S₄………as 1st (upper-most), 2nd, 3rd and 4th sheath from above and taking No, N₁, N₂, N₃………as the upper-most (between the neck-node of a ear and the node of an upper-most leaf), 2nd, 3rd, 4th inter-node from above, B₁ grows simultaneously with S₂ and N₃, and B₂ grows simultaneously with S₃ and N₄, and B₃ with S₄ and N₅, and so forth. Therefore, if B₁ is lengthened, or shortened, S₂ and N₃ are also lengthened or shortened synchronously, and if B₂ is lengthened or shortened, S₃ and N₄ are also lengthened or shortened synchronously. Thus, there are synchronously growing leaf-blades, sheaths and inter-nodes in the growth of rice plants, and so each leaf-blade grows synchronously with its own corresponding sheath and inter-node. 3. When one wants to shorten a given leaf-blade (for instance B₃), one has to restrict the nitrogen supply (by cutting roots or other methods) at or just before the time when the top of that leaf-blade (B3₎ begins to appear from the immediate lower sheath (S₄), and when one wants to lengthen a given leaf-blade (B₃), one ought to top-dress nitrogen at the time when the top of the previous leaf-blade (B₄) begins to appear from the immediate lower leaf-sheath (S₅). When one wants to shorten a given sheath (for instance S₄), one has to reduce thc nitrogen supply at or just before the time when the top of B₃ start to appear from the immediate lower sheath (S₄). 4. By microscopic and anatomical observations the most susceptible developmental stage of a leaf-blade has been found to be the stage II in fig. 3. The stage II is just after the time at which the sheath of a leaf has been differentiated and the sheath as well as the blade are growing most vigorously.

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With the view of (1) clarifying the principles for maximizing yield which can be applied in any sterile field and (2) demonstrating the principles, the authors tried to trace up, on the one hand, the processes determining high yields and, on the other hand, to demonstrate the possibility for obtaining high yields by controlling the growth of plants aiming at an "ideal plant". The characteristics of an "ideal plant" were proposed to be as follows: 1. The plant should have the necessary and sufficient number of spikelets per plant (per unit area) for obtaining a target yield. 2. The plant should be short in culm height as well as in panicle length and many in the number of culms for protecting lodging and increasing the percentage of ripened grains. 3. The upper 3 or 4 leaf-blades of the plant should be short, thick and errect for increasing the percentage of ripened grains (The "leaf-area index" should be nearly 5.). 4. The plant should keep absorbing nitrogen even in the period after heading for increasing the percentage of ripened grains. 5. The plant should have as many green leaves per culm as possible. (The number of green leaves per culm can be considered as an index of healthiness of the plant.) 6. The plant should emerge its heads in early August so that it may possess at least 20 fine days continuously after heading for increasing the amount of photosynthetic products at the ripening stage. On refering to these characteristics, the authors grew rice plants by water-culture and succeeded in obtaining 102 kg per are of brown rice which is much higher than the yield of the first prize in the competition of maximizing yield in 1962 in Japan. As a result of it, the authors proposed to practise the following items for raising the "ideal plant". (1) Use of healthy seedlings for making the plant absorb much nitrogen from the early tillering stage and ensure the necessary number of tillers as early as possible so as to obtain a target yield. (2) Decrease in supplying nitrogen or no supply of nitrogen during the growth stage from 70 to 90 in "leaf-number index" (which is corresponding to nearly 42-18 days before heading) for protecting lodging of the plant and for making the plant short in culm height, panicle length and also leaf length of 3 or 4 upper leaves and for making leaf-blades errect and thick. (3) Making the plant keep absorbing nitrogen even in the period after heading by top-dressing nitrogen just after the stage of reduction division of PMC (meiosis) or at the full heading stage for increasing the percentage of ripened grains. (4) Exclusion of toxic substances in soil by draining for increasing the healthiness of the plant.

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This experiment was undertaken to determine the effect of nitrogen deficiency on the development of tillering bud in rice seedling by water culture method. Design of experiment and composition of nutrient solution are shown in table 1 and 2. Nutrient solution of nitrogen deficiency used for this study omitted the N-ion from the standard nutrient solution (shown in table 2). The results are summarized as follows; In the rice seedling which has been grown under nitrogen deficient condition since the seeding (of rice plant): 1. In case the plant was supplied with nitrogen since the early stage of the 3rd foliage leaf, the 2nd tillering bud grew well. 2. In case the plant was supplied with nitrogen since the early stage of the 4th foligage leaf, the development of the 2nd tillering bud was remarkably inhibited but the 3rd tillering bud grew well. 3. In case the plant was supplied with nitrogen since the early stage of the 5th foliage leaf, not only the development of the 2nd tillering bud but also that of the 3 rd one were remarkably inhibited, but the 4th tillering bud and the following 5th, 6th, 7th etc. showed remarkable growth. 4. In case the plant was grown under nitrorgen deficient condition throghout the whole growing periods of the plant, all the tillering buds in the plant were rested to grow. From these results, the rice seedling which was supplied with nitrogen after having been grown under nitrogen dificient condition in the early growth (of rice plant) it was concluded that the development of tillering buds by the differences of growing stages in the plant supplied nitrogen, were many differences as to the development of tillering bud in the plant, was differently affected in response to the period of nitrogen deficieney, especially the effects on the development of tillering buds in as such low stem-nodes as the 2nd and 3 rd etc. in main stem were remarkable.

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The experiment was undertaken to determine the effect of phosphorus deficiency on the development of tillering bud in rice seedling by water culture method. Design of experiment, composition of nutrient solution, materials and methods of experiment etc. were the same as the previous report. The nutrient solution lacking in phosphorus used for this study omitted the P₂O₅-ion from the standard nutrient solution shown in table 2 in the previous report. The results are summarized as follows; In the rice seedling which has been grown under phosphorus deficient condition since the seedling of rice plant: 1. In case the plant was supplied with phosphorus since the early stage of the 4 h foliage leaf, the 2nd tailoring bud grew fairly well. 2. In case the plant was supplied with phosphorus since the late stage of the 5th foliage leaf, the development of the 2nd tailoring bud was remarkably inhibited but the 3 rd tailoring bud grew well. 3. In case the plant was supplied with phosphorus since the middle stage of the 6 h foliage leaf, not only the development of the 2 d tillering bud but also that of the 3 rd one were remarkably inhibited, but the 4th tillering bud and the following 5th, 6th, 7th etc., showed remarkable growth. 4. In case the plant was grown under phosphorus deficient condition throughout the whole growing periods of the plant, all the tillering buds in the plant were rested to grow. From these results, the effects of phosphorus deficiency on the development of tillering bud in rice seedling were nearly the same as those obtained in the case of nitrogen deficiency, but the degree of the effects in the case of phosphorus deficiency was not so remarkable as those in the case of nitrogen deficiency.

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The experiment was made as to what would be the effect of silicic acid upon the growth of rice plants cultured without supply of silica, when it was applied through their leaf blades. The experiment was designed as follows: Plot non-Si: Rice plants were cultured without supply of silica. Plot spray: Na₂SiO₃ solution (0.1-0.2 ppm, Aug. 23-Sept. 27) was sprayed every other day on the surface of top of the rice plants cultured under the same conditions as rice plants of plot non-Si. Plot Si: Na₂SiO₃ was added in the culture solution. The results obtained were as follows: The rice plants of plot spray were superior to those of the other two plots in the following points; plant height, leaf number, stem number, panicle number, and dry matter weight at harvest time (fig. 1∼5). Contents and percentages of P₂O₅ in the whole plant and each of its organs (except its root) of plot spray were larger than in those of plot non-Si (fig. 7). Total N and P₂O₅ in the rice plant of plot spray were translocated to culms more smoothly than in those of plot non-Si, but not smoothly to panicles (fig. 6∼7). The serious differences of percentages of total N and K₂O among three plots were not found (fig. 6, 8). The number of silicified cells in a leaf blade of the rice plant of plot spray was larger than that of the plant of plot non-Si (table 1), which proves that silica was absorbed in the leaves. Generally, the growth of the rice plant of plot spray were superior than that of the other two plots. The absorbtion of N, P, K through the roots of the rice plants of plot spray was easily; so was the translocation of N, P in the rice plants of plot spray. It is recognized that silicic acid absorbed from the surface of the leaf blade positively affected on the growth and physiological activity of the rice plant. It has need of silicic acid for the good growth of the rice plant.

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This experiment was conducted to clarify the effects of the low temperature (vernalization, particularly) on the shortening of growth period of Italian ryegrass and to know the optimum temperature and days of this treatment. The treatments were combination of a) temperature 0°C and 5°C, b) days 10, 20, 30, 40 days. It was found that 10 days treatments at 0°C and 5°C were little effective, while 20, 30 and 40 days treatments at both temperatures were more effective. The effects were recognized more clearly in the case of 30 and 40 days treatments at both temperatures and the date of initiation of internode elongation was advanced by 7∼11 days. But it has been found that buds and roots in 20 days onward treatments at 5°C grew too long to handle them in the sowing practice. Thus, the good result can be expected, according to this test, from the vernalization of Italian ryegrass for 30, 40 days at 0°C.

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[in Japanese]

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[in Japanese]

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The change in size and structure of mature leaves and their development were investigated in relation to their position on a stem. The size of successive mature leaves on a stem is generally proportionate to the size of shoot apices at the time of initiation of each leaf primordium (length of a mature leaf corresponds to height, and its width to basal diameter of a shoot apex respectively). Such relationship is attained through the course of leaf development affected by the change in height and basal diameter of the shoot apex. The number of vascular bundles in a mature leaf is also found to be closely related to basal diameter of the shoot apex. It can be concluded from these observations that the size and the structure of a leaf are primarily controlled by the size of the shoot apex from which it initiates.

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The experiment was conducted to evaluate the effect of various irrigation methods on the growth and yield of rice plant in direct sowing cultivation. The field experiment involving three irrigation treatments, two levels of nitrogen fertilization and four levels of sowing density was established in 1962. Because of practical consideration in applying irrigation water, the irrigatin treatments were located in separate block. The nitrogen and sowing treatments were randomized in a split plot design with nitrogen levels as the main plot and sowing density as subplot. The replication was three. The irrigation treatments involed three plots of early irrigation, late irrigation and interval irrigation. In the early irrigation plot, the water had been kept 5 cm deep since early tillering stage of rice plant. The late irrigation plot was kept dry during tillering stage of plant, and irrigation was begun when the plant reached young ear formation stage. The interval irrigation plot was applied 5 cm of water in depth at an interval of 7 days. The nitrogen plots were divided into two, that is 0.6 kg and 1.2 kg-N per are. The levels of sowing density were 10, 25, 50 and 100 hills per m². The results obtained are as follows. 1) The amounts of NH₃-N in soil in the plots of both late irrigation and interval irrigation were smaller than that in the plots of early irrigation. The amounts of NO₃-N in soil generally were trace, except the case of late irrigation kept dry through the tillering period of plant. It seems that the decrease of available nitrogen in the late irrigation and interval irrigation plots are caused by the leaching of NO₃-N and the denitrification resulting from the alternation of oxidation and reduction of soil by irrigation and rainfall. 2) The treatments of late irrigation and interval irrigation indicated the increased activity of root, as measured by means of α-Naptylamine, over the early irrigation. The root activity in the high density (100 hills/m²) was lower than that in low density (10 hills/m²). The root weights per unit area in the late irrigation and interval irrigation plots were lighter than that in the early irrigation plot. The treatment of high density indicated the increased weight of root. 3) The grain yields in the late irrigation and interval irrigation plots were about 10 % less than that in the early irrigation plot, while there was little difference between the former two. The grain and total weight at harvest generally increased as the sowing density increased. The highest yield of all treatments was obtained in the plot with early irrigation, heavy nitrogen fertilization and high sowing density combined. The yield data obtained were fitted with rectangular hyperbola equation of the general form: y=x/a+bx where y is the estimated grain or total weight at harvest in kg per are, x is sowing density, and a and b is a coefficient, respectively. The values of two coefficients in both the late irrigation anb interval irrigation are higher than that in the early irrigation, and heavy dose of nitrogen decreased the values of coefficients. It is therefore concluded that the early irrigation method with heavier nitrogen fertilization and higher sowing density is effective for getting high yield of rice.

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