Yoshida - 1981 - Fundamentals of Rice Crop Science

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44 FUNDAMENTALS OF RICE CROP SCIENCE where the climates are similar. The classification of rice varieties by photoperiodic reactions is more rational and should be applicable in a wider range of climates. The following practical grouping is suggested (Vergara and Chang 1976). Reaction to photoperiod Insensitive Weakly sensitive Strongly sensitive Characteristics Very short PSP (less than 30 days) and BVP varying from short to long Marked increase in growth duration when photoperiod is longer than 12 hours; PSP may exceed 30 days but flowering occurs under any long photoperiod Sharp increase in growth duration with increased photoperiod; no flowering beyond critical photoperiod; BVP usually short (not more than 40 days) It should be kept in mind that there is no sharp dividing line between the photoperiod-sensitive and photoperiod-insensitive varieties, and any definition would be based on arbitrary criteria. Table 1.11 lists the photoperiodic reactions for some selected rice varieties and breeding lines. To illustrate a continuous variation in photoperiod sensitivity, the varieties or lines are listed in increasing order of length of PSP. Although the PSP and BVP are shown in Table 1.11, they can be calculated for the variety Peta as follows: BVP = shortest growth duration - 35 = 70 -35 = 35 days (1.10) PSP = longest growth duration - shortest growth duration = 145 -70 = 75 days (1.11) Optimum photoperiod: 10 hours Critical photoperiod: 16 hours e. Agronomic implications of photoperiodism. Photoperiod-insensitive varieties can flower and ripen throughout the year provided irrigation water is available. Thus, the use of photoperiod-insensitive varieties makes the planning of rice cultivation more flexible and more suitable to the multiple cropping systems characteristic of progressive agriculture. On the other hand, the photoperiod sensitivity of rice varieties continues to be a useful characteristic under certain environments. Floating rice is planted early in the season when the soil can still be worked. It matures when the annual flood waters recede, about 180-200 days after sowing. A variety with such a long growth period must be photoperiod sensitive. So far, there is no known tropical variety that has a long growth period and is insensitive to photoperiod (Vergara and Chang 1976).
GROWTH AND DEVELOPMENT OF THE RICE PLANT 45 Table 1.12. Yield of traditional tropical rices in relation to transplanting time. a Variety Yield b (kg/ha) July August September October November Bangkhen 293 229 3478 4791 b 3386 2435 Luang Tawng 101 67 2455 4121 3098 2234 Nang Mon S-4 155 2222 2971 2010 1174 Puang Nahk 16 4136 4104 4769 3492 2388 Jao Luang 11 158 1791 3571 2120 2681 Khao Dok Mali 105 66 1219 3031 3020 1820 Bai Lod 104 388 1758 3519 2241 2019 Khao Pak Maw 17 265 1537 3820 2187 1528 a Takahashi et al (1967). b ltalic figures indicate highest yields. Photoperiod sensitivity may function as a safety mechanism when the onset of the rainy season is considerably delayed (Oka 1958). In most of tropical Asia, the onset of the rainy season is unpredictable and varies from year to year, whereas its end is fairly fixed. Thus, when planted late, a photoperiod-sensitive variety may still mature at its usual time regardless of shortened growing periods. On the other hand, a photoperiod-insensitive variety requires a specific growing time before flowering, and hence, maturity. Thus, such a variety will suffer from water stress at later growth stages after the rain ceases. Most traditional rice varieties in the tropics are sensitive to photoperiod, have long maturity periods, and are tall. When they are grown with high levels of applied nitrogen, they tend to lodge at later growth stages, and their grain yields are extremely low. When these varieties are planted later than usual, they have a shorter growth duration and usually are shorter in height, and consequently, have increased lodging resistance. Table 1.12 shows the results of delayed-planting experiments using photoperiod-sensitive varieties. The September transplanting, 2 months later than usual, gave the highest yield for all varieties. Delayed planting of photoperiodsensitive traditional indica rice varieties prevented excessive growth and lodging, and resulted in high grain yields. 1.8.2. Response to temperature a. The temperature summation concept. Temperature summation is a summation of daily mean temperatures over a certain period of growth or development. When the temperature drops to a certain level, growth or development may stop. Temperatures below this threshold are considered ineffective. TWO ways of calculating temperature summation have been used for rice (Asakuma 1958, Copeland 1924, Nagai 1962): Temperature summation = S (Daily mean temperature) (1.12) Temperature summation = S (Daily mean temperature - threshold temperature). (1.13)
Page 3 and 4: FOREWORD Rice is vital to more than
Page 5 and 6: CONTENTS Foreword Preface GROWTH AN
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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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