Yoshida - 1981 - Fundamentals of Rice Crop Science

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PHYSIOLOGICAL ANALYSIS OF RICE YIELD 243 Table 7.3. Yield and yield components of rice crops grown in solution culture and in the field at Konosu, Japan. a Water culture Soil culture Grain yield (t/ha) Brown rice 10.2 5.8 Rough rice 12.7 7.2 Yield components Panicles (no./m 2 ) 699 379 Spikelets (no./panicle) 75 05 Spikelets (no./m 2 ) 52.4 × 10 3 32.2 × 10 3 Ripened grains (%) 89.5 83.2 1,000 grain wt (g) 26.5 25.7 a Adapted from Matsushima et al (1963). • None of the toxic substances produced under reductive conditions are present (e.g. hydrogen sulfide, excess ferrous iron, and organic acids). • No organic matter (humus) is present. Thus, water culture provides a convenient means of controlling plant growth through the supply of plant nutrients, and of testing whether soil fertility is essential to high yields (Matsushima et a1 1963, Matsushima 1976). An experiment to compare water culture with soil culture used wooden boxes 10 m 2 and 20 cm deep, lined with vinyl sheets and filled with gravel. Rice plants of the same variety were grown in water culture in the boxes and in soil culture in the field at similar planting densities. Ample nitrogen, phosphorus, and potassium and about 23 t compost/ha were applied to the field. Both crops were grown under the same weather conditions. The water culture produced 12.7 t/ha and soil culture, 7.2 t/ha (Table 7.3). The grain yield difference, caused by the difference in rooting media, is evidence that soil fertility per se is not indispensable for high yields. It also suggests that the toxic substances produced in the soil hampers high yields under certain conditions. In fact, adequate percolation and drainage are considered essential for high yields because they remove toxic substances from the soil. 7.5.3. Agronomic management An analysis of Japan's No. 1 prize winners' rice cultivation technology suggests that the component technologies alone may not always give good results (Shiroshita 1963, Togari 1966). However, their combination as a package is important in achieving high yields. a. Choice of lodging-resistant variety, adequate planting density, and proper plant protection. To achieve high yields, it is essential to use a lodging-resistant variety. Close spacing assures a LAI sufficiently large for maximum crop photosynthesis and the production of a large number of panicles to meet the requirements for yield components of high yielding crops. Diseases, insect pests, and weeds must be carefully controlled. b. Deep plowing. The depth of the surface soil ranges from 15 to 21 cm among the prize winners’ fields, and from 9 to 12 cm among most farmers' fields. A deep
244 FUNDAMENTALS OF RICE CROP SCIENCE 7.8. Relationship between plowing depth and cation exchange capacity (CEC) of high yielding paddy fields that produced more than 7.5 t/ha (Aomine 1955). surface soil allows rice roots to contact the soil nutrients in a larger volume of soil. Deep plowing improves soil properties by drying the lower soil layers, thereby, promoting the weathering of soil minerals. However, deep plowing may not be effective unless combined with increased applications of fertilizer. A large soil volume implies a greater supply of soil nutrients and a greater capacity for cation exchange. In paddy soils, applied nitrogen is held by soil clay minerals through cation exchange. In soils whose cation exchange capacity (CEC) is low, more of the applied nitrogen comes into the soil solution. The rice plant can absorb this nitrogen easily and its early growth becomes vigorous. At later growth stages, the rice crop may suffer nitrogen shortages because a considerable portion of the applied nitrogen has already been absorbed and also some nitrogen may have been lost by percolation. An adequately high CEC will hold applied nitrogen and release it to rice at later growth stages. When plowing depths are plotted against CEC in fields that produce yields higher than 7.5 t/ha, the CEC tends to increase at shallower plowing depths (Fig. 7.8). Thus, if the CEC is sufficiently large, a shallow surface soil can produce a high yield. From Figure 7.8, and on the basis of highly simplified assumptions, such a CEC is estimated at 250 kg equivalent/ha. c. Heavy application of compost. To produce high yields, the prize winners applied from 8 to 30 t compost/ha. The application of large amounts of compost is usually combined with deep plowing and good internal drainage. Compost releases nitrogen at slower rates than do chemical fertilizers and thus provides nitrogen at later stages of crop growth. Composts or farmyard manures are good sources of nutrients such as phosphorus, potassium, and silica. Deep plowing in well-drained fields quickly decreases the organic matter in the surface soil. A liberal application of compost will help maintain the organic matter supply. However, compost is not essential for a high yield (see Section 7.5.2). Moderately high yields can be obtained without compost and on soils low in organic matter. There is no added benefit in terms of yield between nitrogen added as ammonium sulfate and that provided partially with 10 t compost/ha, if the
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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
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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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