Yoshida - 1981 - Fundamentals of Rice Crop Science

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RICE PLANT CHARACTERS IN RELATION TO YIELDING ABILITY 221 6.5. Number of panicles and paddy weight in relation to planting density (Yamada 1963). 6.4. GROWTH DURATION The growth duration of a variety is highly location and season specific because of interactions between the variety's photoperiod and temperature sensitivity and weather conditions. Thus, terms such as early, medium, and late maturing are meaningful only under particular locations or seasons. Traditional tropical varieties in Asia are well adapted to the monsoon season. They are usually planted in June or July, take 160–200 days to mature, and are harvested in November or December. Such long-growth duration varieties are inevitably photoperiod sensitive. In a limited area of tropical Asia, however, irrigation is available and rice can be grown in the dry season, normally from January to May. This is called the off-season or dry season crop. Varieties adapted to the dry season are photoperiod insensitive and mature in 90–130 days. Varieties of too short growth duration may not produce high yields because of limited vegetative growth, and those of too long growth duration may not be high yielding because of excessive vegetative growth, which may cause lodging. About 120 days from seeding to maturity appears to be optimum for maximum yield at high nitrogen levels in the tropics. However, a longer growth duration may produce higher yields when fertility is low (Kawano and Tanaka 1968) presumably because there is more time to extract soil nitrogen.
222 FUNDAMENTALS OF RICE CROP SCIENCE Table 6.4. Effect of spacing on grain yield and daily production of 3 varieties, IRRI, 1970. a Daily grain production Growth Grain in main Selection Spacing duration yield field (cm) (days) (t/ha) (kg/ha) Wet season IR747B2-6 5 × 5 95 5.62 10 × 10 95 4.70 lR22 20 × 20 95 4.15 5 × 5 114 4.92 10 × 10 114 5.01 IR8 20 × 20 114 4.57 5 × 5 124 5.32 10 × 10 124 5.31 20 × 20 124 5.14 Dry season IR747B2-6 10 × 10 98 7.92 20 × 20 98 7.23 75 63 55 52 53 41 51 51 49 102 93 10 × 10 110 7.23 80 IR154-18-2-1 20 × 20 110 6.98 78 IR8 20 × 20 132 8.61 77 a IRRI (1971). Early maturing varieties allow intensified cropping. At conventional spacing, short growth duration varieties usually give low yields because of insufficient vegetative growth. Close spacing is essential for early maturing varieties to achieve high yields (Table 6.4). In the wet season the grain yield of IR747B2-6 at 5 × 5 cm is as high as that of IR8. In the dry, IR747B2-6 produces about 8 t/ha at 10 × 10 cm, whereas IR8 gives 8.6 t/ha at 20- × 20-cm spacing. At close spacings therefore, the yield potential of IR747B2-6 can be nearly as high as that of IR8. One clear benefit of early maturing varieties is high grain production per day. In both wet and dry seasons, IR747B2-6 is about 30% more efficient than IR8 in daily grain production. Another advantage of an early maturing variety is high water-use efficiency. As illustrated in Chapter 2, paddy field evapotranspiration is proportional to incident solar radiation and, hence, nearly proportional to the number of days the crop is in the field. Thus, a higher daily production implies a higher water-use efficiency. How far can growth duration be shortened without sacrificing yield potential? Panicle development is fairly fixed at about 30 days. The duration of ripening depends on temperature; it is about 30 days in the tropics. Thus, about 60 days is necessary for reproductive growth and ripening in the tropics. How many days are needed for vegetative growth? Although difficult to answer experience suggests that about 30 days is minimum for sufficient vegetative
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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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Yoshida - 1981 - Fundamentals of Rice Crop Science

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