Yoshida - 1981 - Fundamentals of Rice Crop Science

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7.1. CONTRIBUTION OF ACCUMULATED CARBOHYDRATE TO THE GRAIN Carbohydrates such as sugars and starch begin to accumulate sharply about 2 weeks before heading and reach a maximum concentration in the plant’s vegetative parts, mainly in the leaf sheath and culm, at around heading. The concentration begins to decrease as ripening proceeds and may rise again slightly near maturity (Fig. 7.1). Direct, qualitative evidence that the accumulated carbohydrates are translocated into grains was obtained with a 14 C technique (Murayama et al 1961, Oshima 1966). The accumulated carbohydrate has three possible functions in grain production: • To supply a portion of the grain carbohydrate. • To support sustained grain growth under variable weather conditions. • To stabilize grain yield under unfavorable weather conditions during ripening. The usual method for calculating the contribution of accumulated carbohydrates to the grain analyzes carbohydrates in the vegetative parts and uses the following formula: Contribution (%) of accumulated carbohydrate = to grain carbohydrate (CHO) F -(CHO) M × 100, (CHO) G (7.1)
232 FUNDAMENTALS OF RICE CROP SCIENCE 7.1. Changes in the amount of temporarily stored carbohydrates( preheading storage) and dry weight of various parts according to growth stages in rice (schematic illustration, Murata and Matsushima 1975). where ( CHO ) F = carbohydrate present in the vegetative part at flowering, ( CHO ) M = carbohydrate present in the vegetative part at maturity, and ( CHO ) G = carbohydrate in the grain at maturity. Estimates by the above method range from 0 to 71%, depending on the cultural practices, nitrogen application, and growth duration. Under most conditions the estimate falls between 0 and 40%. However, 71% was obtained when the plant density was extremely high — 146 hills/m 2 (Wada 1969). The percentage contribution will become high if the grain carbohydrate is small, which may result when grain filling is disturbed by unfavorable weather conditions. The above calculation assumes that all the carbohydrates lost from vegetative parts during grain filling will be translocated to the grains. This assumption is obviously wrong. Some portion of the stored carbohydrate must be used in respiration during grain filling. Hence, the formula tends to overestimate the contribution of accumulated carbohydrates to the grains. The 14 C technique allows a more accurate estimate. The stored carbohydrates in the vegetative parts can be labelled with 14 C by feeding the rice crop with 14 CO 2 about 10 days before flowering. The contribution of photosynthesis during ripening can be estimated by calculating the difference between the total grain carbohydrate and the carbohydrates attributed to preheading storage. Figure 7.2 shows that 68% of the accumulated carbohydrate was translocated into the grain, 20% was respired during the ripening period, and 12% remained in the vegetative parts. The amount of the carbohydrate translocated was equal to about 21% of the grain carbohydrate, or the equivalent of about 2 t grain/ha when the yield was 7.8 t/ha. Equation 7.1 gave an estimate of 34% in the same experiment. When photosynthesis during ripening is restricted by 90% shading, the accumulated carbohydrate supports grain growth at almost a normal rate for about 2 weeks
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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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Page 203 and 204: 5.1. PHOTOSYNTHESIS 5.1.1. Photosyn
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Page 257 and 258: Table 7.6. An example of high yield
Page 261 and 262: REFERENCES AGRICULTURAL POLICY STUD
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Yoshida - 1981 - Fundamentals of Rice Crop Science

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