Yoshida - 1981 - Fundamentals of Rice Crop Science

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RICE PLANT CHARACTERS IN RELATION TO YIELDING ABILITY 225 had a mean value of 1.13 (Table 6.6). The grain-straw ratio of 6 low nitrogenresponsive varieties had a mean value of 0.56. In the above example, the nitrogen responsiveness is largely related to plant height, which in turn is related to lodging resistance and harvest index or grainstraw ratio. A high harvest index is characteristic of the new high yielding varieties, but it may be the result of conscious selection for short, stiff straw rather than for large grain yield with the minimum production of total dry matter (Thorne 1966). A tall variety could have a high harvest index if the panicle is larger (Tanaka 1972a). At the moment, however, it is difficult to find a tall rice variety with a high harvest index. 6.5.3. Growth duration vs harvest index Harvest index is inversely correlated with growth duration (Fig. 6.7). The correlation, however, appears quite loose. 6.5.4. Growth duration vs plant height Plant height at flowering is positively correlated with growth duration (Fig. 6.8). Again, this correlation is very loose. For a growth duration of about 80–90 days, plant height is scattered over a wide range from less than 100 cm to about 200 cm. In general, the amount of growth is the product of rate and time: Growth = rate × time (6.2) If the growth rate is sufficiently high to compensate for a short duration, the rice plant can produce a large amount of growth. This is likely to be true for height growth. For example, Dular, a 100-day variety, is as tall as Mahsuri, a 134-day variety (IRRI 1977). 6.7. Relation between growth duration and harvest index (Tanaka et al 1966)
226 FUNDAMENTALS OF RICE CROP SCIENCE 6.8. Relation between growth duration and plant height (Tanaka et al 1966). 6.6. CHANGES IN MORPHOLOGICAL CHARACTERS OF RICE VARIETIES The morphological character that has contributed most to high yields is a short, stiff culm that gives lodging resistance (Shigemura 1966, Chandler 1968). Changes in the morphological characters of rice varieties that became commercially available between 1905 and 1962 in Hokkaido, Japan, indicate that varieties have been selected for shorter plant height, higher tillering capacity, and more erect leaves (Fig. 6.9). Increasing LAI is associated with higher tillering capacity. Shorter plant height (lodging resistance) and higher tillering capacity (increasing LAI) would have contributed more to increased yield and nitrogen response than a smaller foliar absorption coefficient. The crop photosynthesis model suggests that leaf angle (foliar absorption coefficient) is not too important up to a LAI of 3–4 (Monteith 1965, Duncan 1971, van Keulen 1975). A similar trend is also observed for rice varieties in southern Japan (Ito and Hayashi 1969). Historically, the selection must have been based on selection for yield with liberal use of nitrogen fertilizers and improved cultural practices such as close spacing. However, the outcome of this selection agrees with the present knowledge of the physiological aspects of high yields in transplanted rice. 6.7. MODIFICATIONS OF VARIETAL TRAITS FOR SUBNORMAL CONDITIONS Under subnormal management conditions, high yielding varieties may or may not be good yielders. The recent recognition of diverse environments in rice-growing regions indicates the need for a better understanding of the benefits and disadvantages of contrasting plant characters (Yoshida 1977b, 1978). With such informa-
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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 203 and 204: 5.1. PHOTOSYNTHESIS 5.1.1. Photosyn
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Page 207 and 208: Photosynthetic characteristics Meas
Page 223 and 224: A traditional tall variety vs an im
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Page 257 and 258: Table 7.6. An example of high yield
Page 261 and 262: REFERENCES AGRICULTURAL POLICY STUD
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Yoshida - 1981 - Fundamentals of Rice Crop Science

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