Yoshida - 1981 - Fundamentals of Rice Crop Science

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3.1. SOIL SUBMERGENCE AND RICE NUTRITION An ample water supply is probably the greatest advantage of soil submergence for irrigated rice. Unstable production of rainfed lowland and upland rice crops is largely attributed to water shortages. Submergence creates a unique environment for rice’s growth and nutrition. The root environment during submergence is characterized by a lack of oxygen and subsequent series of reductive changes; the exchange of gases between soil and air is markedly curtailed. Within a few hours after submergence, microorganisms use up the oxygen present in the water or trapped in the soil (Fig. 3.1). After the disappearance of the molecular oxygen, carbon dioxide and organic acid levels increase sharply. The amounts of methane and molecular hydrogen increase gradually because of the anaerobic microbial activity. To avoid suffocation of root tissues in submerged soils, the rice plant has developed special tissues through which air is transported from shoot to root. This subject will be discussed in the succeeding section. In submerged soils, ammonia is the major form of nitrogen available for rice. Although relatively low concentrations of ammonia are toxic to many upland crops, rice tolerates and uses ammonia efficiently at relatively high concentrations. An increase in the availability of phosphate is an obvious benefit of soil submergence. Thus, the application of phosphate is less vital to lowland rice than to upland rice and other upland crops. Phosphate applications, however, are
112 FUNDAMENTALS OF RICE CROP SCIENCE 3.1. Course of microbial metabolism in waterlogged paddy soil during incubation in syringe at 35°C. Before an arrow: facultative anaerobic metabolism; after an arrow: strictly anaerobic metabolism (Takai and Kamura 1966). important when soils have a high capacity to fix phosphate, when temperature is unfavorably low for rice growth, and where little or no phosphate fertilizer has been applied in the past. Concentrations of phosphorus, potassium, iron, manganese, and silicon increase in the soil solution after soil submergence. The concentration of zinc, however, decreases. The increase in ferrous iron concentration is often excessive, inducing iron toxicity in rice. Under upland conditions, weeds, particularly those having the C-4 pathway, grow vigorously and compete with rice for light and nutrients. Submergence curtails weed growth (Tanaka, I. 1976).
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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 69 and 70: 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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