Yoshida - 1981 - Fundamentals of Rice Crop Science

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CLIMATIC ENVIRONMENT AND ITS INFLUENCE 71 2.3. Monthly mean temperatures at 4 places of different latitudes in Asia. An important characteristic of tropical and temperate climates is obtained by comparing seasonal variations and diurnal changes in temperature. In the temperate regions, the annual range exceeds the daily range; in the tropics, the daily range is greater than the annual range. At Los Baños, Philippines, the diurnal temperature variation ranges from 7.1°C in December to 11.0°C in April, compared with a maximum variation of 4.1°C in the year's monthly mean temperatures. At Singapore, the annual temperature range is about 2.2°C, while the diurnal range reaches 6.2°C. This characteristic of the tropical climate is described by the well-known saying: the nights are the winter of the tropics. Temperature always goes down as elevation increases. The decrease of temperature attributable to altitude is about 0.6°C/100 m in the lowest 1.5 km of the atmosphere (Lockwood 1974). Thus temperature at any elevation in the tropics may be estimated by the following formula: Temperature at high elevations = Temperature at sea level – 0.6 h, (2.4) 2.4. Change in the amplitude of daily temperature (°C) variation with distance from the ocean. Latitude about 40°C; elevations not over 500 m. Numerals indicate locations of stations. Station 1 is an island. Station2 is at the coast (from an Introduction to Climate by G. T. Trewartha 1968. Copyright © 1968 by McGraw-Hill. Inc. Used with the permission of McGraw-Hill Book Company.)
72 FUNDAMENTALS OF RICE CROP SCIENCE where temperature is in degrees centigrade, and h is the altitude above sea level in hectometers. For example, if a monthly mean temperature at sea level is 30°C, the corresponding temperature at 1,000 m above sea level would be 24°C. While the above equation gives an easy way to estimate temperature at a given elevation under most conditions, it must be used with caution because the local variations of the temperature drop with elevation are sometimes quite large. 2.3.2. Critical low and high temperatures Extreme temperatures are destructive to plant growth and, hence, define the environment under which the life cycle of the rice plant can be completed. The critically low and high temperatures, normally below 20°C and above 30°C, vary from one growth stage to another (Table 2.4). These critical temperatures differ according to variety, duration of critical temperature, diurnal changes, and physiological status of the plant. Subjecting the rice plant to temperatures below 20°C at about the reduction division stage of the pollen mother cells usually induces a high percentage of spikelet sterility (Satake 1969). Differences among rice varieties in response to low temperatures at this stage have been clearly demonstrated. When Norin 20, a susceptible variety, was held at 15°C for 4 days, 51% of the spikelets were sterile. Hayayuki, a tolerant variety, under the same conditions produced only 5% sterile spikelets. Temperatures as low as 12°C will not induce sterility if they last for only 2 days, but will induce about 100% sterility if they last for 6 days. Low temperature-induced sterility is normally attributed to low night temperatures. High day temperatures, however, appear to alleviate the effects of low night temperatures (see Table 2.7). When the plant was subjected to a constant night Table 2.4. Response of the rice plant to varying temperatures at different growth stages. a Growth stage Critical temperature b (°C) Low High Optimum Germination Seedling emergence and establishment Rooting Leaf elongation Tillering Initiation of panicle primordia Panicle differentiation Anthesis Ripening 10 12–13 16 7–12 9–16 15 15–20 22 12–18 45 35 35 45 33 – 38 35 30 20–35 25–30 25–28 31 25–31 – – 30–33 20–25 a Adapted and modified from Yoshida (1977a). b Refers to daily mean temperature except for germination.
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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 29 and 30: 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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