Yoshida - 1981 - Fundamentals of Rice Crop Science

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NUTRITIONAL DISORDERS 179 Table 4.1. Fertilizer trial with IR8 at 2 locations in West Pakistan, 1966. a Grain yield (t/ha) N-P 2 O 5 -K 2 O (kg/ha) at Dokri at Kala Shah Kaku 0-0-0 0-45-45 34-45-45 67-45-45 101-45-45 134-45-45 5.61 5.74 7.14 5.48 8.77 5.15 9.24 5.57 9.25 4.90 10.27 4.94 a Yoshida et al (1970). 4.3. DIAGNOSTIC TECHNIQUES 4.3.1. Visible symptoms (Tanaka and Yoshida 1970, Yoshida 1975a) a. What to observe. Symptoms are one way plants communicate; they are a kind of language. When plants are deficient in a nutrient or suffer toxicity of an element or substance, visible symptoms show up. A systematic method of observing the major plant parts—plant height, tillers, leaves, and roots—is advisable if visible symptoms are used for diagnosing nutritional disorders. Plant height. Stunted growth is a common symptom for deficiency or toxicity. Unusually tall plants may be induced by Bakanae disease. Tillers. Reduced tiller number is a common symptom for deficiency or toxicity. Leaves. Chlorosis, necrosis (brown spots), and orange discoloration are common symptoms of deficiency or toxicity. The mobility of nutrients within the plant and the position of the leaf on which the deficiency symptoms appear are interrelated. For a nutrient whose mobility is low, symptoms normally appear in upper leaves because the nutrient fails to move from lower to upper leaves where it is needed for active growth. Iron, boron, and calcium are examples of low mobile nutrients. On the other hand, when a nutrient is mobile, symptoms normally appear in the lower leaves. The lower leaves suffer nutrient deficiency because the nutrient is translocated upward. Nitrogen, phosphorus, potassium, and sulfur are examples of mobile nutrients. Symptoms of element toxicity normally appear in the lower leaves, where the absorbed element accumulates more. Iron, manganese and boron toxicity symptoms appear first in the lower leaves. There are two kinds of chlorosis: interveinal and uniform. Potassium and magnesium deficiencies cause interveinal chlorosis, whereas nitrogen and sulfur deficiencies produce chlorosis uniformly in the leaves. Roots. When shoot growth is impaired, root growth is also poor because both are closely connected. Therefore, scanty root growth alone may not mean much.
180 FUNDAMENTALS OF RICE CROP SCIENCE Root color is affected by age (see Chapter 1) and soil iron content. A root is white when young and actively growing. When it is long and old, and when there is adequate iron in the soil, it is normally brown because of iron oxide deposits on the root surface. When the iron content in the soil is low, however, old roots remain white, pale, or grayish. Under extremely reductive conditions some roots or an entire root system becomes black, suggesting hydrogen sulfide injury. These roots turn brown when they are exposed to air. Roots and the soil mass from flooded soils may have a hydrogen sulfide smell. Hydrogen sulfide can be detected by using a piece of filter paper that has been impregnated with saturated basic lead acetate solution. b. When to observe symptoms. The early stages of symptom development are the best time for observing visible symptoms. It is of little value to observe plants when the symptoms of the disorder have become so severe that the plants are almost dead. Zinc deficiency in lowland rice usually appears within 2–3 weeks after transplanting or sowing. Later, the crop may recover spontaneously. When the deficiency is severe, plants may die or the symptoms may persist until flowering or longer. The problem field appears patchy because some plants die early while others survive and grow. Iron toxicity symptoms may appear on plants grown on sandy soils adjacent to lateritic highlands 1–2 weeks after transplanting. Symptoms may also appear 1–2 months after transplanting and persist until flowering when iron toxicity occurs in peaty or boggy soils. c. Deficiency symptoms Nitrogen. Plants are stunted with limited tillers. Except for young leaves which are greener, leaves are narrow, short, erect, and yellowish green. Old leaves die when light straw colored. Phosphorus. Plants are stunted with limited tillers. Leaves are narrow, short, erect, and dirty dark green. Young leaves are healthy and old leaves die when brown colored. A reddish or purplish color may develop on the leaves if the variety has a tendency to produce anthocyanin pigment. Potassium. Plants are stunted, but tillering is only slightly reduced. Leaves are short, droopy, and dark green. The lower leaves at the interveins, starting from the tip, turn yellow and, eventually, dry to a light-brown color. Sometimes brown spots may develop on dark-green leaves. Sulfur. The symptoms are very similar to and almost impossible to visually distinguish from those of nitrogen deficiency. Calcium. The general appearance of the plant is little affected except when the deficiency is acute. The growing tip of the upper leaves becomes white, rolled, and -curled. In an extreme case, the plant is stunted and the growing point dies. Magnesium. Height and tiller number are little affected when the deficiency is moderate. Leaves are wavy and droopy due to expansion of the angle between the leaf blade and the leaf sheath. Interveinal chlorosis, occurring on lower leaves, is characterized by an orangish-yellow color.
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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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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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