Yoshida - 1981 - Fundamentals of Rice Crop Science

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PHYSIOLOGICAL ANALYSIS OF RICE FIELD 239 The constant 1,000-grain weight of a given variety does not mean that individual grains have the same weight per grain. Individual grain weights vary to some extent but the mean value is constant (Fig. 7.4). The term ripened grains has been used in Japan to distinguish between commercially useful grains and chaff. The ripened grains are those that are heavier than salt water with a specific gravity of 1.06 (Matsushima 1970). For indica rices, specific gravity values of 1.10–1.12 are tentatively suggested (Osada 1974). 7.4. COMPARISONS OF GRAIN YIELDS ACHIEVED BY DIFFER- ENT LEVELS OF TECHNOLOGY 7.4.1. Yield changes associated with technological changes — the Japanese experience In 900 AD, the average yield of brown rice in Japan was approximately 1 t/ha. In 1868, the year of the Meiji revolution, which was the dawn of modern Japan, it was about 2 t/ha. Thus, it took about 1,000 years to double the average yield (Ishizuka 1969). The introduction of irrigation systems is believed to have contributed to higher yields and to have laid the ground work for further progress in agricultural technology after the Meiji Revolution. The yield increased to about 3 t/ha before chemical fertilizers were introduced around 1930 (Fig. 7.5); compost and other kinds of organic matter were the major sources of added plant nutrients up to that time. In 1954, the yield increased to 4 t/ha, i.e., the yield doubled in less than 100 years. Heavy applications of nitrogen fertilizers after World War II caused many changes in variety, plant protection, soil improvement, and cultural management. The high national average yield in Japan today has been realized through the integration of technology. 7.4.2. Grain yield comparison among national average, experiment station’s record, and the highest yield From 1949 to 1968, Japan’s No. 1 rice yield contest was held to encourage Japanese farmers to produce more rice. In 1960, 13.2 t/ha was recorded in this contest. It was the highest yield ever achieved in Japan (Agricultural Policy Study Commission 1971). National average yields increased from 3.88 t/ha in 1949 to 5.51 t/ha in 1968. Long-term weather-assessment field trials have been conducted for many years at agricultural experiment stations in Japan. These experiments assess the effects of yearly weather fluctuations on rice yields, using the same cultural practices. A comparison of rice yield from various sources, summarized in Figure 7.6, indicates: • The national average yield is very similar to the weather-assessment trial yields recorded at agricultural experiment stations. • The highest yields achieved by farmers are more than two times greater than the national average regardless of weather conditions.
240 FUNDAMENTALS OF RICE CROP SCIENCE 7.5. Rice yields in Japan, 1910–1940 (Ishizuka 1969). Although each farmer uses different cultural practices, the average farmer’s technology can be approximated by the technology adopted in the weatherassessment trials. In these trials, plants were spaced 23.4 × 23.4 cm (18.2 hills/m 2 ), and nitrogen applications included basal dressing at 60 kg/ha and topdressing at 15 kg/ha. The usual plant protection and weeding practices were followed. Thus, yields of about 5 t/ha were achieved with these practices under 7.6. Comparison of the highest recorded rice yields, weather-assessment trial yields, and the national average yields in Japan from 1949 to 1968.
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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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