Yoshida - 1981 - Fundamentals of Rice Crop Science

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PHYSIOLOGICAL ANALYSIS OF RICE YIELD 245 Table 7.4. Comparison of rice yields in dry and wet seasons with ammonium sulfate alone and with partial substitution of nitrogen with compost (average from the 10th crop, 1969 dry season, to the 23rd crop, 1975 dry season, IRRI). a Paddy yield Season Nitrogen application (kg/ha) (t/ha) Dry 140 b Compost (10 t/ha = 24) + 116 b 7.43 7.23 Wet 60 b c 4.74 Compost (10 t/ha = 24) + 36 b 4.80 a Tanaka (1978). b Asammonium sulfate. c 140 kg N/ha only in 1973. supply of other nutrients is favorable (Table 7.4). When aiming at high yields, however, it is advantageous to build soil fertility. Compost or other kinds of organic matter supply nitrogen to rice plants throughout growth. This continuous nitrogen supply favors high yields by preventing excessive vegetative growth and lodging. Furthermore, it is difficult to simulate such a condition by manipulating fertilizer nitrogen without the help of soil organic matter (Tanaka 1978). d. Adequate percolation and drainage. High yields can be better achieved on well-drained fields. Although high rates of percolation cause nutrient loss, adequate rates may remove toxic substances from the rooting zone and prevent excessive soil reduction. A percolation rate of 15–25 mm/day is considered adequate in Japan. In Figure 7.9, the lower line indicates that grain yield decreases with increasing percolation rates. The upper line indicates that high yields are obtained at a percolation rate of about 15 mm/day. Percolation rates faster than 15 mm/day decrease yield. Why this is true is not well understood. Most likely percolation removes some toxic substances such as hydrogen sulfide, ferrous iron, and organic acids (Takijima and KOnnO 1959, Takijima 1960). If the above explanation is correct, it follows that a certain amount of percolation would benefit rice growth only in soils where injurious substances accumulate to levels toxic to rice. e. Drainage and intermittent irrigation. Drainage and intermittent irrigation, commonly practiced by the prize winners, implies that water is drained until the soil surface is exposed to air, after which irrigation water is reintroduced. The rate of drainage and the interval between the cycles vary with soil characteristics and weather conditions. This practice is believed to remove toxic substances and maintain healthy roots under reductive soil conditions (Agricultural Policy Study Commission 1971, Togari 1966). Table 7.5 shows that drainage and intermittent irrigation treatment increases the root-shoot ratio and improves root growth. f. Soil dressing. Incorporation of clayey hill soils into paddy fields is also a common practice to improve soil fertility. Hill soils at early stages of weathering supply various bases, silica, and iron that have been depleted by intensive, continuous rice cropping. Soil dressing increases the depth of the surface soil
246 FUNDAMENTALS OF RICE CROP SCIENCE 7.9. Daily field water requirement and rice yield (Isozaki 1967 as cited by Nakagawa 1976). Average evapotranspiration rate of irrigated rice fields in Japan is approximately 5 mm day. Therefore, the daily field water requirement minus 5 mm day would approximately represent the daily percolation rate. layer; it may increase water-holding capacity and CEC. More nitrogen and phosphorus than usual should be applied when soil dressing is practiced because hill soils are low in these nutrients. Soil dressing has been practiced by progressive farmers but it is quite laborious. An alternative way to improve soil properties is to apply bentonite clay (10–15 t/ha) or zeolite (5–10 t/ha). Bentonite, largely composed of montmorillonite, has a high CEC and, hence, increases the nitrogen-holding capacity of sandy soils. Bentonite can minimize excessive percolation because of its swelling characteristic. Zeolite is a powdered tuff that has a high CEC (80–160 meq/100 g) and does not swell in water like bentonite (Dei 1978, Shiga 1969). 7.5.4. Examples of high yielding technology A systematic study at the Central Agricultural Experiment Station, Konosu, Japan, attempted to achieve high yields (Shiroshita et al 1962). The Konosu clay loam soil at the station is representative of alluvial soils derived from the Arakawa River in Kwanto Plain. The clay is mainly composed of allophane with small amounts of kaolinite, vermiculite, and illite. The CEC is about 15 meq/100 g soil. Table 7.5. Effect of intermittent irrigation and drainage on root growth. a Maximum Roots (no) at soil depth of root Root Root- Treatment length dry shoot 0–10 10–20 20–30 30–40 40–50 50–60 60–70 (cm) wt (g) ratio cm cm cm cm cm cm cm Flooded 48.7 7.48 6.0 416 135 73 39 7 0.5 0 Intermittent 77.8 8.79 12.5 463 293 141 74 38 28 11 irrigation and drainage a Dei (1 978).
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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 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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