Yoshida - 1981 - Fundamentals of Rice Crop Science

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NUTRITIONAL DISORDERS 187 Table 4.8. Methods for available soil nutrients. a Nutrient Methods of analysis N P Incubation method Bray-Kurtz No. 2 method K Exchangeable form Si 1N Na-acetate (pH 4.0) extraction B Hot water Cu DTPA + CaCI 2 (pH 7.3) Fe DTPA – CaCI 2 (pH 7.3) NH 4 -acetate (pH 4.8) Mn DTPA + CaCI, (pH 7.3) 0.1 N H 3 PO 4 and 3 N NH 4 H 2 PO 4 Mo NH 4 -oxalate (pH 3.3) Zn 0.05 N HCI Dithizone + NH 4 -acetate EDTA + (NH 4 ) 2 CO 3 DTPA + CaCI 2 (pH 7.3) a Kawaguchi and Kyuma (1977) for macronutrients; Randhawa et al (1978) for micronutrients. band to a chlorotic leaf. Within a week, the band will become green if the chlorosis is due to iron deficiency. For suspected zinc deficiency, 1 or 2 plants may be sprayed with a 0.1% aqueous solution of zinc sulfate or zinc chloride with a small amount of sticker. If the symptoms are due to zinc deficiency, the plant will begin to recover in a week or so. 4.4.2. Greenhouse experiment A small amount of soil may be collected from the problem field and tested under controlled conditions in the greenhouse for various means of correcting the problem. Potted conditions in the greenhouse may differ from field conditions. For example, pot experiments in the greenhouse occasionally fail to reproduce symptoms while the problem field suffers severe zinc deficiency. In such a case, the addition of cellulose powder assures the reproduction of zinc deficiency by aggravating the problem (Yoshida and Tanaka 1969). 4.4.3. Field experiment A final assessment of the diagnosis and the practical means of correcting the problem must be tested at the problem site. Various forms and amounts of chemicals, and methods and times of application can be tested by the field experiment (Yoshida et al 1971, 1973). The diagnosis is assumed to be correct when the treatment corrects the problem. The cause-effect relationship is thus established. This may not always be true, however. In the alkali soil areas of California, a severe chlorosis called alkali disease occurs on water-sown rice. The symptoms are indicative of iron deficiency caused by high pH. In field experiments, the application of ferric sulfate was
188 FUNDAMENTALS OF RICE CROP SCIENCE effective in curing the chlorosis (Mikkelsen et al 1965). Later experiments, however, revealed that chemically pure ferric sulfate failed to cure alkali disease, whereas commercial ferric sulfate, which contained small amounts of zinc, corrected the problem. In a separate treatment, a small amount of zinc cured the alkali disease (Brandon et al 1972). Now, zinc deficiency is well recognized in the same area where iron deficiency was previously reported though the two may not be completely identical (Mikkelsen and Brandon 1975). The same happened when zinc deficiency of California citrus was studied about 40 years ago (Hoagland 1944). 4.5. CORRECTIVE MEASURES FOR NUTRITIONAL DISORDERS When the cause or causes of a nutritional disorder is properly identified, cure is the next step. However, detailed discussions of corrective measures are beyond the scope of this book. This section, therefore, will briefly examine the three major approaches to correcting nutritional disorders: • Agronomic methods • Soil improvement • Varietal improvement 4.5.1. Agronomic methods When the cause of a nutritional disorder is a nutritional deficiency, the problem is usually cured by applying the deficient nutrient. For example, zinc deficiency can be corrected by dipping seedling roots in a 2% ZnO suspension, the foliar application of zinc sulfate, and applying various zinc compounds to the soil. Similarly, sulfur deficiency can be easily corrected by applying various kinds of sulfur-containing materials (Aiyar 1945). An elegant way of correcting sulfur deficiency, however, is to apply ammonium sulfate as a partial replacement for urea (Mamaril et al 1979). The suitability of a particular agronomic technique for a given region depends not only on the effectiveness of the method under given soil conditions but on the availability, price, and cost-benefit ratio of chemicals. 4.5.2. Soil improvement A toxicity problem is perhaps more difficult to correct than a deficiency problem, particularly when the toxicity is attributed to the inherent soil environment. When the salt concentration reaches a certain level in the soil, salinity can be cured only by desalinization measures. Hydrogen sulfide injury in sandy, degraded soils can be. partially corrected with nonsulfur fertilizers such as urea. However, incorporating hill soils that supply large quantities of ferric iron oxide to the soil is more effective. 4.5.3. Varietal improvement There are some degrees of varietal difference in tolerance for toxicities and deficiencies. Recently, an intensive effort has been made to improve plant toler-
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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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