Yoshida - 1981 - Fundamentals of Rice Crop Science

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62 FUNDAMENTALS OF RICE CROP SCIENCE Table 1.15. The model yield components of IR8 in the cloudy wet season and in the sunny dry season. a Component Wet season Dry season Panicle number per m 2 250 375 Spikelet number per panicle 100 100 Total number of spikelets per m 2 25,000 37,500 Filled spikelets (%) 85 85 1,000-grain wt (g) 29 29 Expected grain yield (t/ha) 6.16 9.24 a Chandler (1969). The model yield components of transplanted IR8 are shown in Table 1.15. To produce a yield of 6 t/ha in the cloudy wet season, the required number of spikelets per square meter could be obtained if plants are spaced at 20 × 20 cm (i.e., 25 plants/m 2 ), and each plant produces 10 panicles with 100 spikelets/ panicle. Under most weather conditions, 85% filled spikelets is normally expected and the 1,000-grain weight is usually a stable varietal character. Since equation 1.20 is a kind of arithmetic computation and since each component, particularly the first three, is dependent on others. one cannot increase each yield component at his discretion. For instance, when the number of panicles per square meter is increased by using a high plant density, the number of spikelets per panicle is decreased. A comparison of direct-seeded rice and transplanted rice gives a good example of such a relationship (Yoshida and Parao 1972). It is relatively easy to obtain from direct-seeded rice 600 panicles/m 2 , which is twice the number normally obtained from good transplanted rice. The number of spikelets per panicle, however, is much smaller for the direct-seeded rice. As a result, the total number of spikelets per square meter may be about the same for rice grown under the two cultivation systems. Maximum yield is predetermined by the potential of a variety and the environment. A computation of yield components would be meaningful for designing a blueprint of the target yield and examining the defects of a given crop if a comparison is made with a crop that has already achieved a good yield under a similar environment. Each yield component is determined at a particular stage in the plant's life (Matsushima 1970). In the transplanting rice cultivation, the number of panicles per square meter is largely dependent on tillering performance, which is largely determined by 10 days after the maximum tiller number stage. In the directseeding system, however, the number of panicles per square meter is largely dependent on seeding rate and percentage of emergence. The number of spikelets per panicle, on the other hand, is determined during the reproductive growth stage. Early in the reproductive growth, the maximum number of spikelets is determined by the differentiation of branches and spikelets. After spikelet differentiation, some spikelets may degenerate. The number of spikelets observed at heading or at
GROWTH AND DEVELOPMENT OF THE RICE PLANT 63 maturity is the difference between the number of differentiated primordia and the number that degenerate. The percentage of filled spikelets is determined before, at, and after heading. Unfavorable weather conditions, such as low or high temperatures at about reduction division stage and anthesis, may induce sterility. Unfavorable weather conditions during ripening may hamper continued growth of some spikelets, resulting in unfilled spikelets. The 1,000-grain weight is a stable varietal character because the grain size is rigidly controlled by the size of the hull. Hence, grain cannot grow to a size greater than that permitted by the hull no matter how favorable weather conditions and nutrient supply are. The size of the hull, however, is subject to slight modifications by solar radiation during the 2 weeks before anthesis. In summary, weather conditions, cultural management, and nutrient supply greatly influence each yield component. Understanding their interrelationships is a key to improvement in rice yield.
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FOREWORD Rice is vital to more than
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CONTENTS Foreword Preface GROWTH AN
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3.2. Adaptation to Submerged Soils
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4.5. Corrective Measures for Nutrit
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1 .1. OUTLINE OF THE LIFE HISTORY T
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GROWTH AND DEVELOPMENT OF THE RICE
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5.1. PHOTOSYNTHESIS 5.1.1. Photosyn
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PHOTOSYNTHESIS AND RESPIRATION 197
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Photosynthetic characteristics Meas
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A traditional tall variety vs an im
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Table 7.6. An example of high yield
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REFERENCES AGRICULTURAL POLICY STUD
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Yoshida - 1981 - Fundamentals of Rice Crop Science

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