Yoshida - 1981 - Fundamentals of Rice Crop Science

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PHYSIOLOGICAL ANALYSIS OF RICE YIELD 247 The water table of the field used in this experiment was 80 cm below the soil surface in winter and 18 cm in summer. The rice grain yield is usually around 4.5 t/ha. The researchers found that a low number of sunshine-hours during ripening resulted in a low percentage of filled spikelets. To overcome this problem, they shifted the crop season 1 month earlier. Component technologies included drainage, deep plowing, and application of 19–56 t compost/ha (Table 7.6). AS a consequence, applied nitrogen exceeded 400 kg/ha. There was not much difference in grain yield between the treatments when the field was poorly drained. When the field received adequate drainage, grain yield increased from 6.6 to 10.0 t/ha. Another example of high yielding technology is the intensive use of topdressing. Nitrogen topdressing is normally done at panicle initiation or flag-leaf stage in Hokkaido, Japan. Shiga and Miyazaki (1977) studied the nitrogen absorption process of a high yielding crop and simulated that process by topdressing. Nitrogen topdressing was given 5 times between panicle initiation and heading, and the amount of nitrogen applied each time was increased stepwise from 5 kg N/ha at panicle initiation to 10 kg N/ha 5 days later, to 15 kg N/ha after another 5 days after that, to 30 kg N/ha at flag-leaf stage (15 days after panicle initiation), and 30 kg N/ha at heading. By this technique, grain yield was increased from 3.8 t/ha without fertilizer nitrogen to 9.7 t/ha with a simulated topdressing. The simulated topdressing produced high yields of more than 8.8 t/ha over 5 years. 7.6. FACTORS LlMlTlNG THE PRESENT YIELD PLATEAU Improving grain-filling is one way to increase grain yield. The filled-spikelet percentage is about 85%, even under favorable conditions, which means that grain yield might be increased by 15%. Of the 15% unfilled spikelets, however, around 5–10% are unfertilized, and difficult to eliminate. An increase in photosynthesis (source activity) relative to spikelet number (sink size) would probably increase filled-spikelet percentage by only 5–10% and, hence, yield by a similar degree. Thus, the yield to be achieved by improving gain-filling would be much lower than the estimated potential yield. It is possible to increase yield by increasing the number of spikelets per unit of land area. In other words, it is important to increase yield capacity when yield capacity is defined as the product of spikelet number and potential weight per grain. To examine this possibility, it must be known whether grain filling, as determined by the amount of solar radiation during ripening, is already limiting to yield. The question implies that the number of spikelets per unit of land area may be increased through improved cultural practices or by genetic manipulation, but a considerable portion of the spikelets produced may remain unfilled because of limited solar radiation. In Japan. the percentage of ripened grains decreases when the number of spikelets per square meter is increased (Matsushima 1970, Wada 1959). Thus,
Table 7.6. An example of high yielding cultivation technology attempted at the Central Agricultural Experiment Station in Well-drained 12 75 18.8 18.8 0 0 112.6 6.06 6.67 12 75 18.8 18.8 18.75 97.5 210.1 6.92 8.12 18 75 18.8 18.8 18.75 97.5 210.1 6.18 7.91 18 75 18.8 18.8 37.50 195.0 307.6 6.92 8.29 18 75 18.8 18.8 56.25 292.5 405.1 8.58 11.13 18 112.5 18.8 18.8 56.25 292.5 442.6 10.02 12.05 112.6 210.1 210.1 307.6 405.1 442.6 6.00 6.74 6.29 6.67 6.47 6.1 7 6.68 7.55 7.06 7.93 8.20 8.20 Japan. a Depth of Field drainage plowing (cm) Amt of N applied (kg/ha) Basal Tillering Panicle initiation Compost N equiv. t/ha (kg/ha) Total amt of N applied (kg/ha) Grain (t/ha) Straw (t/ha) Poorly-drained 12 12 18 18 18 18 75 18.8 18.8 75 18.8 18.8 75 18.8 18.8 75 18.8 18.8 75 18.8 18.8 112.5 18.8 18.8 0 0 18.75 97.5 18.75 97.5 37.50 195.0 56.25 292.5 56.25 292.5 a Shiroshita et al (1962). Early planting; variety Kin-maze, 1958.
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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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66 FUNDAMENTALS OF RICE CROP SCIENC
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5.1. PHOTOSYNTHESIS 5.1.1. Photosyn
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Page 223 and 224: A traditional tall variety vs an im
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Page 261 and 262: REFERENCES AGRICULTURAL POLICY STUD
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Yoshida - 1981 - Fundamentals of Rice Crop Science

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