Yoshida - 1981 - Fundamentals of Rice Crop Science

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MINERAL NUTRITION OF RICE 131 3.8a. Relation of relative tillering rate (RTR) with nitrogen content of the leaf blade (Yoshida and Hayakawa 1970). b. Relationship between RTR and phosphorus content of the leaf blade (Yoshida and Hayakawa 1970). c. Relationship between RTR and potassium content of the leaf blade (Yoshida and Hayakawa 1970). the primordium develops into a tiller depends on such factors as the nutritional status of the plant, the supply of carbohydrate, and the light and temperature conditions. Tillering is highly impaired by nitrogen or phosphorus deficiency. Hence, the nutrient status of the plant should be related to tillering performance. Because there is always a tiller primordium at each node of a shoot, the increase in tiller number per unit time should be proportional to the total number of tillers present (Yoshida and Hayakawa 1970): (3.14)
132 FUNDAMENTALS OF RICE CROP SCIENCE where N is number of tillers, t is time, and r is a constant. The solution for the equation 3.14 is: r = log e N 2 – log e N 1 2.303 (log 10 N 2 – log 10 N 1 ) = t 2 – t 1 t 2 – t 1 (3.15) The constant r is called the relative tillering rate (RTR) on the analogy of the relative growth rate. Equation 3.14 can be rewritten as: dN 1 RTR = × (3.16) dt N Thus, RTR can be considered the mean tillering rate per tiller and used as a quantitative measure for the relationship between mineral nutrition and tillering. As shown in Figure 3.8a and b, the RTR is closely correlated with nitrogen, phosphorus, and potassium content in the leaf blades. Tillering stops when nitrogen content in the blade becomes 2.0%, phosphorus 0.03%, and potassium 0.5%. The tillering rate increases linearly with an increasing nitrogen content of up to 5%. With phosphorus, the tillering rate increases up to about 0.2%, above which an increase in phosphorus has no effect on tillering. Similarly, potassium content as high as 1.5% increases the tillering rate. The critical phosphorus concentration for tillering appears to be affected by temperature. Tiller number per square meter increases with an increasing phosphorus content of up to 0.35% in rice crops grown in Hokkaido, Japan, where low temperatures prevail (Shiga et al 1976). Such a high phosphorus requirement can be a reason why phosphate applications are particularly beneficial in cool years in Hokkaido. An examination of tillering is one useful way to examine the growth status of a rice crop. When tillering is retarded by a nutrient shortage, growth parameters such as leaf area and dry weight also decrease (Table 3.13). The table also illustrates that any nutrient whose content is below optimum level limits overall growth even though other nutrients are present in sufficient quantities. 3.6 MINERAL NUTRITION AND PHOTOSYNTHESIS Nutrient content is related to the photosynthetic activity of leaves because essential nutrients are directly or indirectly involved in photosynthesis and respiration. For example, nitrogen is a constituent of proteins which, in turn, are constituents of protoplasm, chloroplasts, and enzymes. Phosphorus as inorganic phosphate, an energy-rich phosphate compound, and a coenzyme, is directly involved in photosynthesis. Potassium is involved in opening and closing the stomata that control carbon dioxide diffusion into green tissues, a first step in photosynthesis (Fujino 1967, Fischer and Hsiao 1968). Potassium is also essential in activating enzymes such as starch synthetase (Nitsos and Evans 1969). The relative photosynthetic rate of leaf blades is positively correlated with their nutrient content (Fig. 3.9). The critical nutrient contents for a high leaf photo-
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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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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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