Yoshida - 1981 - Fundamentals of Rice Crop Science

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CLIMATIC ENVIRONMENT AND ITS INFLUENCE 109 Table 2.17. Yield of variety Jaya under 3 levels of submergence (25, 50, 75% of crop ht) at each of the 3 growth phases during aman (Jul–Nov) and boro (Jan–Apr). 1973–74. a Relative grain yield (%) Plant growth stage Ht of plant 1973 submerged (%) (aman) Control (continuous submergence 5 ± 2 cm) 100 Seedling establishment 25 82 to maximum tillering 50 75 75 68 Maximum tillering to 25 81 flowering 50 71 75 72 Flowering to maturity 25 79 50 76 75 70 a Adapted from Pande (1976). 1974 (boro) 100 75 62 58 74 64 56 71 66 50 c. Submerged areas. The water level and duration are variable but the plants are usually completely submerged. In some areas submergence occurs almost every year. In many lowland rice fields submergence occurs only during typhoons or unusually heavy, continuous rains. Attention is currently focused on improving rice varieties adapted to flood areas by incorporating the elongation genes of floating rice into improved semidwarf high-yielding varieties. These new varieties, called deepwater rices, can remain short when the water is shallow and grow tall in response to increased water depths (Jackson et al 1972). A large portion of the rainfed lowland rice area falls into the category of submerged areas, where partial submergence is the common problem. When a rice crop is submerged to different degrees at different growth stages, the grain yield decreases in different proportions. For example, with 25% plant height submergence at tillering, yield decreases by 18% in aman and 25% in boro; with 75% submergence at ripening, yield decreases by 30% in aman and 50% in boro (Table 2.17). The yield-decreasing effects of partial submergence could be attributed to impaired tillering and decreased area of photosynthetic leaf surface. To overcome the adverse effects of partial submergence on grain yield, varieties with intermediate plant height (about 110–130 cm, taller than semidwarfs and shorter than traditional tall varieties) are replacing semidwarf varieties in shallow water areas that are subject to occasional floods. 2.6. ANNUAL PRODUCTIVITY IN TEMPERATE REGIONS AND THE TROPICS In temperate regions, one or two rice crops can be grown annually. In the tropics, three to four crops a year are possible, provided irrigation is available. Thus, rice
110 FUNDAMENTALS OF RICE CROP SCIENCE Table 2.18. Annual productivity of rice in temporate regions and in the tropics. a Location Crop Season Yield (t/ha) Hokkaido, Japan (43°N) Kagawa, Japan (34°N) May-October March-July July-October 6.5 5.5 5.4 10.9 Okinawa, Japan (27°N) January-June June-August September-November 6.2 4.9 4.2 15.3 Los Baños, Philippines (14°N) a Yoshida (1977a). January-May May-July July-October October-December 8.5 4.9 5.9 4.4 23.7 yield can be compared in two ways: on a per-crop basis and on an annualproduction basis. The maximum recorded yield per crop in Japan was 10.5 t brown rice/ha, which is equivalent to 13.2 t rough rice/ha (Agricultural Policy Study Commission 1971). In the tropics, rice variety IR24 yielded 11.0 t/ha in the dry season in Los Baños, Philippines (IRRI 1973), and IR8 produced 10.7 t/ha at Battambang, Cambodia (Hirano et al 1968). The highest recorded rice yield in India is 17.8 t/ha in Maharashtra State (Suetsugu 1975). Thus, on a yield-per-crop basis, tropical areas are no less productive than the temperate regions. In terms of annual rice production, the tropics has a distinctly greater potential than the temperate regions. In Hokkaido, Japan, where only 1 crop a year is grown, about 6.5 t/ha was obtained in a normal year (Table 2.18). In this region, low temperature is often a major cause of crop failure; hence, rice yield is unstable depending on weather conditions. In southern Japan, 2 crops yielded a total of about 11 t/ha in 1 year. In Okinawa, the southernmost part of Japan, a field experiment recorded 15.3 t/ha from 3 crops. And, in the Philippines, about 24 t/ha were recorded for 4 crops a year. These data clearly indicate that the potential annual rice productivity is much higher in the tropics than in the temperate regions. In practice, however, continuous rice cropping may not be advisable because of severe disease and insect problems. However, the tropical environment for rice cultivation at any time of the year provides great flexibility in planning rice production.
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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 67 and 68: 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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