This study examined the influence of relative humidity of the atmosphere on the dry matter production of rice at its seedling stage. The plants were grown in a growth cabinet where the relative humidity was maintained at either 60% (dry treatment), 75% (standard treatment), or 90% (wet treatment) with the day/night temperature of 28/24°C and the illumination of 34-30 klux. The plants grown in a more humid atmosphere produced more dry matter when compared over the same growing period after seeding. But, no difference was detected when compared at the same plant age measured in the number of leaves (Fig. 1). We investigated the characteristics of the leaf blade and leaf sheath and conducted grow h analysis. 1. The top to root ratio was greater in the plants grown in a more humid atmosphere when measured either on the same day after seeding or at the same plant age (Fig. 2). 2. Atmospheric humidity had little effect on the weight and length of the leaf blade. On the other hand, the weight and length of the leaf sheath were strongly influenced: the more humid the atmosphere was, the greater the weight and length of leaf sheaths. 3. With increasing atmospheric humidity, the leaf area increased and the specific leaf area increased: the specific leaf area showed a significant positive correlation with the leaf area (Fig. 4). 4. The leaf area index, which strongly influenced crop growth rate, was larger in a more humid atmosphere, which may be why the dry matter production was higher in a more humid condition when compared at the same growing period (Table 2). 5. The plants grown in a more humid condition had a larger leaves. However they were thinner and had a lower photosynthetic rate (Fig. 6). Therefore, it seemed that there was no difference in the dry matter production of the plants grown in the three different humidifies when compared at the same plant age.

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Eight varieties differed in ear type were used in this study: Stirpe 136 and Anthocyane (javanica) (ear type I: Number of grains on the secondary rachis-branch was abundant in the basal position of ear), Jaekeon (japonica) and Milyang No. 23 (japonica-indica hybrid) (ear type II: number or grains on the secondary rachis-branch was less near panicle base than in ear type: I), Norin No. 8(japonica) and Josaeng Tongil(japonica-indica hybrid) (ear type III: number of grains on the secondary rachis-branch was abundant in the middle position of ear) and Dojinkyo and Panbila (indica) (ear type V: number of grains on the secondary rachis-branch was abundant in thc upper position of ear). After harvesting, number of the primary rachis-branches per ear, and number of grains on the primary rachis-branch, and number or the secondary rachis-branches and their grains at each node of rachis were determined for the ear of the longest stem in the hill in twenty replicates. Under the same level of fertilizer, increase in planting density decreases number of the primary rachis-branches per ear, and the secondary rachis-branches and their grains at all the nodes of rachis, especially, at the basal position of ear. These trends seemed to be intensified by increase in fertilizer level in almost all the varieties (Fig. 2 A-H). Because of the extreme decrease of number of the secondary rachis-branches and their grains at the basal position of ear as mentioned above, Stirpe 136, Anthocyane and Milyang No. 23 changed their ear type, II to III in high fertilizer and dense planting plot (Fig. 2 A, B and C). In the previous experiment which was undertaken under favourable climates for the rice cultivation, Stirpe 136 and Anthocyane, Jaekeon and Panbila showed ear type I, II and V, respectively. However, there existed no those ear types in the present experiment. These may be due to decrease of number of grains on the secondary rachis-branch at the basal (Stirp 136, Anthocyane and Jaekeon) and upper (Panbila) positions, which appeared to have been caused by the low temperature during the present study (Fig. 1). Anthocyane and Panbila were used for determination of ear type in all the tillers of four hills as influenced by fertilizer level and planting density. Number of the primary rachis-branches per ear, number of the secondary rachis-branches and their grains at each node of rachis were determined as for the ear having every different number of the primary rachis-branches per ear in four hills in four replicates. Number of the secondary rachis-branches and their gains decreased at all the nodes of rachis, especially, at the basal position of ear, with reduction of number of the primary rachis-branches per ear. This caused changes in ear type of cars having reduced number of the primary rachis-branches per ear, viz. ear type II to III and further, in some cases, to ear type IV in the hill of Anthocyane (Fig. 3A), but ears of Panbila showed ear type IV or V in all the plots differing in fertilizer level and planting density (Fig. 3B). Increase in fertilizer level and planting density decreases number of the secondary rachis-branches and their grains at all the nodes of rachis, especially at the basal position of ear. For this reason, number of secondary rachis-branches and their grains was almost zero at the panicle base in the plots of high fertilizer level and dense planting density, regardless of number of the primary rachis-branches per ear. Anthocyane and Panbila showed ear type II and IV in the ears with the largest number of the primary rachis-branches, respectively. Number of grains on the primary rachis-branch at almost all the nodes of rachis was about 6 in all the plots, varieties and tillers.

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The grain growth of rice is highly tolerant to water stress throughout the grain-filling period. Despite a large reduction in dry matter production, the grain growth during both the period of active cell division and expansion, and the subsequent period of rapid starch deposition was little affected by water deficits. Reduction in dry matter production due to water stress was almost completely compensated by the increased transfer of reserved assimilates to the grain. But, the plants which experienced drought during the early stage of grain growth and were relieved from the stress thereafter yielded less than the plants which were well watered throughout the grain-filling period. Similar response was observed in wheat, and a deteriorated root function in stressed plants is suggested as a possible factor for this reduced grain yield. It is therefore probable that the yield reduction in rice associated with prolonged drought during the period of grain-filling is a result of the indirect effects of water stress through the function of roots with regard to the production of hormonal substances. However, in view of the highly tolerant nature of the short term grain growth to water deficits, it is more likely that the lack of assimilate supply to the grain is responsible for reduced grain yield in plants under prolonged stress, since there must be an upper limit to the amount of pre-anthesis reserves that can be available for grain growth. This situation has been clearly demonstrated with maize. The objective of this study was to examine the above premise, i.e., the total assimlate supply is the primary factor that controls grain yield in rice droughted during most of the grain-filling period. Rice plants (Oryza sativa L. cv. Nipponbare) were grown in wooden trays (1.05×1.20×0.15 m) containing sandy silt soil. The trays were placed in a vinyl-covered house located in a field and so arranged to form a block of miniature crops that simulates a field density of 95, 200 plants/10a. Part of the block was adequately watered throughout the whole growing period, while water application to the remaining block was restricted after ear emergence so that leaf water potential around midday was maintained at -10 to -15 bars. At intervals during the treatment period, water potential was measured on the flag leaves between 1300 and 1500 hours. During this period, areas of green leaves and grain growth were also monitored. Dry weights of grains, shoots and roots were determined both at the time of ear emergence and at maturity. Daytime water potential in the leaves of stressed plants declined rapidly after the start of treatment, reaching -12 bars 10 days after ear emergence (Fig. 2). Leaf water potentials in the control plants remained at -3 to -6 bars except at the later stage of the growth. Leaf senescence was accelerated in stressed plants, LAI reaching less than 50% of the initial value by the 20th clay after ear emergence, whereas the controls still retained the green leaves of about 60% of the initial value until the full-ripe stage (Fig. 3). Water deficits reduced the dry matter production by approximately 40% (Tables 2 and 3) through the reduction in both the leaf area duration and the average rate of dry matter production (Table 4). Despite this, the grain yield of desiccated plants was only reduce by 16% (Tables 1 and 2), due to the increased assimilate transfer from the shoots to the grain (Tables 2 and 3). Thus the apparent contribution of reserves to grain yield was 34% in the desiccated plants, about three times as high as in the controls (Table 3.). These findings are in agreement with our earlier studies; the grain growth for the first 10 to 20 days after ear emergence was only slightly affected by the water stress (Fig. 4). However, the rate of grain growth declined as the water stress was prolonged. [the rest omitted]

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Effect of nitrogen side-dressing at 10 days after flowering on yield, yield components and protein content of seeds was examined using 12 varieties and ammonium sulfate. 1. Mean yield among 12 varieties supplemented with 120 kg nitrogen per ha increased by 6.7 percent or 250 kg per ha (Table 1). The most affected variety was Chippewa (13.2%) and the least was Waseshiroge (0.1%) (Fig. 1). 2. As to the early or medium varieties, yield increase was mainly due to the increase of 100 seeds weight. As to the late varieties, on the other hand, it was mainly due to the increase of pod number (Fig. 1). 3. Nitrogen or protein content of seeds increased by 3.3 percent on the average of 12 varieties supplemented with 120 kg nitrogen per ha. Protein yield per unit land area increased also by 10.3 percent (Table 2). 4. Effect on yield of supplemental nitrogen was the largest on the least fertile plots, and vice versa. On the least fertile plots all of the yield components, pod number, number of seeds per pod and 100 seeds weight increased. On the most fertile plots, on the other hand, pod number decreased, which negated the increase of 100 seeds weight, hence the least yield increase (Fig. 3). 5. Taking into account of the increase of total revenue due to the increase of yield and input cost for ammonium sulfate and labour for its dressing, the most reasonable amount of supplemental nitrogen was supposed to be around 100 kg per ha. In this case the increase of net revenue was about 35, 000 yen per ha.

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In order to identify the factors which have played a significant role in the increase of rice yield, comparative growth analysis was attempted for several cultivars of rice plant which have been cultivated in the past or currently being cultivated in the south-western part of Japan (Kyushu district). Dry matter production of old and new types of rice cultivars was compared in the field. The old types refer to the ear-weight-type with long culms, vs. the new types or ear-number-type with short culms. The results obtained are as follows: During the growth period before heading, dry matter production was higher in thc old types than in the new types of cultivars (Table 2). This difference was due to the production of dry matter during the ear initiation stage. Dry matter increase was positively correlated with canopy height in this stage (r=0.858^**) (Fig. 2). Further analysis indicated that the canopy of the old types consisted of lower leaf area density as compared to that of the new types of cultivars (Fig. 3). As a result, dry matter increase showed a significant negative correlation with the leaf area density (r=-0.852^**) (Fig. 4), suggesting a possible correlation between CO₂ diffusion and a vertical distribution of leaf area in the canopy. During the growth period after heading, dry matter increase showed a significant positive correlation with the leaf area index (LAI) and net assimilation rate (NAR)(Fig. 5). The new types which showed higher LAI and NAR produced a larger amount of dry matter as compared to the old types of cultivars (Fig. 5). Also, the new types had higher nitrogen content in the leaf blade and lower decrease in thc photosynthetic rate (p₀) and leaf area during ripening stage than the old types of cultivars (Fig. 6, Table 4). The old types of cultivars experienced lodging during the middle and later ripening stages whereas red-kernel rice, regarded as a very old type of cultivar, showed lodging at heading, due to the presence of a long culm. In order to increase dry matter production and hence grain yield, the role of canopy height should be reevaluated in relation to dry matter production both before and after heading.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Formation and morphology of the primary roots on growing shoots were observed in field grown cereals, i.e. Setaria italica Beauv., Panicum miliaceum L., Echinochloa frumentacea Link., Pennisetum typhoideum Rich., sorghum bicolor Moench., Coix lachrymajobi L. and Eleusine coracana Gaertn. All species showed a similar developmental pattern. Although root emergence proceeded keeping pace with leaf emergence, the pace varied from species to species. Among species we also found some morphological differences such as, stem diameters, the number and diameters of the primary roots, and frequency of the secondary roots along the primary root axes. In all species examined, the basal diameter of the primary roots was closely correlated with the diameter of the stem on which they appeared. The root diameter acropetally decreased rapidly in any root parts where the diameter is large. The results were discussed from two aspects, namely, the determining process of the number of the primary roots and formative process of each primary root.

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The factors of the occurrence of straighthead of rice plants are vague yet. The purpose of this paper is to present the effects of the application of barley straws in common paddy fields on the occurrence of the straighthead of rice plants. The summary of the results is shown below. 1) Some plants with high percentage sterility occured in the test plots in which barley straws had been applied. 2) Numerous plants with high percentage sterility occured in the barley straws applied paddy field which was restored to the paddy field last spring after ten years use as an upland. 3) Abnormal rice plants with deformed panicles and spikelets occured in the test plot in which barley straws were applied two years before. Percentage sterility of them were high (Fig. 4). 4) Abundant typical symptoms of straighthead of rice plants were observed in a farmer's paddy field in which much barnyard manure had been applied. 5) From above-mentioned results, it was concluded that straighthead of rice plants occured not only in paddy fields which had been restored after at least more than several years use as uplands but also in common paddy fields in which much organic matter such as barley straws had been applied.

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In order to clarify the roles of EF (epidermis-cortical fiber compound) and P (fundamental parenchyma) in breaking resistance, several dynamic characteristics of the fourth internode from the top of rice culm, var. Koshihikari, were studied at the time of harvesting. Breaking strength and deflection of PEF (whole internode tissues) and P, obtained by shaving off the EF from PEF, were measured with aid of the stalk bending hardness tester (type EO-III). Tensile strength, compressive strength and shearing strength were measured by traditional methods used in the material testing. These data are shown in Table 1. Some calculations with these data verify that EF/P ratio in YOUNG's modulus, tensile strength and compressive strength are 113, 63 and 19, respectively. Besides, the tensile strength of EF in rice internode was ascertained to be almost the same to that of the xylem tissue of boxwood (Buxes microphylla var. suffruticosa Makino). Moreover, about 89% of bending stress (tensile and compressive stress) is supported with EF, and about 78% of shearing stress is supported with P in the bended internode. Therefore, with regard of bending stress, the internode of rice culm can be considered dynamically to be a pipe composed of thin EF as illustrated in Fig. 1. The value of maximum stress M can be obtained by the formula (6), and d²t [(diameter of internode)²×(thickness of EF)] can be considered to be a very important factor in breaking resistance. On the other hand, the main role of P in breaking resistance is to prevent sectional deformation and to maintain cylindrical form in the bended internode. Breaking strength of the fourth internodes with or without leaf sheath was investigated in the ripening period as shown in Fig. 2. The breaking strength had a peak soon after heading and a minimum at 25-30 days after heading. It may be thought that the slight increase in breaking strength at the time of harvesting was caused by reaccumulation of starch in the internode.

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The carbon budget and efficiencies of solar energy utilization for gross and net production of rape plant populations have been calculated from data on diurnal courses of CO₂ exchange and dry matter production. This was done both for individual days at different growth stages and for the whole growth period. The results arc summarized as follows: 1. The daily gross production (Pg), derived from data on diurnal courses of. CO₂ exchange, increased gradually during early stages of growth. At the beginning of bolting (early March), Pg began to increase steeply attaining to a maximum at the beginning of ripening (early May) and then decreased rapidly. The largest value of Pg was 61.53 g CO₂/m²/day (Table 1, Fig. 1). 2. The daily net production (Pn) varied with growth stage in a manner similar to Pg althought the maximum occurred a little earlier than that for Pg. The largest value obtained was 41.14g CO₂/m²day (Table 1, Fig. 1). 3. The Pn/Pg ratio, as well as Pg and Pn, varied largely as a result of changes in daily solar radiation (S). That is, the ratio increased with increasing S approaching a certain level asymptotically. 4. The level of the Pn/Pg ratio, calculated for fine day at each growth stage, remained around 70% during the period from the earliest growth stage to the beginning of ripening and then decreased rapidly. The ΣPn/ΣPg ratio (ΣPn and ΣPg denote total net and gross production for the whole growth period) was fairly constant and fell in the range of 53-56% in the three season's experiments. 5. The efficiencies of solar energy utilization for Pg(Eg) and for Pn(En), based on total solar radiation incident of the field, were high on cloudy days and low on clear days. As for the developmental changes in these efficiencies, it was observed that maxima appeared in the period from the middle of flowering to the beginning of ripening. The averages for days during this period, which included various weather conditions, were 0.85% and 0.47% respectively (Table 4). 6. The proportion of seed to total net production (ΣPn) on a calorie basis was 36%. Oil content of seed on a calorie basis was 62%. Thus, efficiencies of solar energy utilization for seed yield and oil production, based on total solar radiation incident on the field during the whole growth period, were estimated as 0.162% and 0.101% respectively (Table 4). 7. The results of analysis of the yield production process of rape were compared with those from other crops. The authers concluded that it is particularly important in the case of rape plant to promote development of the leaf canopy at early growth stages to increase the interception of solar radiation.

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