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Handbook of Plant Nutrition - chapter 13

13 Molybdenum Molybdenum was discovered in 1778 by the Swedish chemist, Carl Wilhelm Scheele. However, its importance in biological systems was not established until 1930 when Bortels discovered that molybdenum was essential for the growth of Azotobacter bacteria in a nutrient medium. | CRC_DK2972_Ch013.qxd 6 6 2006 1 13 PM Page 375 13 Molybden um Russell L. Hamlin Coggins Farms and Produce Lake Park Georgia CONTENTS 13.1 Historical Information .375 13.1.1 Determination of Essentiality.375 13.1.2 Function in Plants .376 13.1.2.1 Nitrogenase .376 13.1.2.2 Nitrate Reductase .377 13.1.2.3 Xanthine Dehydrogenase .377 13.1.2.4 Aldehyde Oxidase .378 13.1.2.5 Sulfite Oxidase .378 13.2 Diagnosis of Molybdenum Status of Plants.378 13.2.1 Deficiency .378 13.2.2 Excess.379 13.2.3 Molybdenum Concentration and Distribution in Plants .379 13.2.4 Analytical Techniques for the Determination of Molybdenum in Plants .382 13.3 Assessment of Molybdenum Status of Soils .382 13.3.1 Soil Molybdenum Content.382 13.3.2 Forms of Molybdenum in Soils .384 13.3.3 Interactions with Phosphorus and Sulfur.385 13.3.4 Soil Analysis .386 13.3.4.1 Determination of Total Molybdenum in Soil .386 13.3.4.2 Determination of Available Molybdenum in Soil.386 13.4 Molybdenum Fertilizers .387 13.4.1 Methods of Application .387 13.4.1.1 Soil Applications .387 13.4.1.2 Foliar Fertilization.388 13.4.1.3 Seed Treatment .388 13.4.2 Crop Response to Applied Molybdenum .388 References .389 13.1 HISTORICAL INFORMATION 13.1.1 Determination of Essentiality Molybdenum was discovered in 1778 by the Swedish chemist Carl Wilhelm Scheele. However its importance in biological systems was not established until 1930 when Bortels discovered that molybdenum was essential for the growth of Azotobacter bacteria in a nutrient medium 1 . Subsequently 375 CRC_DK2972_Ch013.qxd 6 6 2006 1 13 PM Page 376 376 Handbook of Plant Nutrition in 1936 Steinberg determined that molybdenum was required for the growth of the fungus Aspergillus niger 2 . The essential nature of molybdenum for higher plants was first reported by Arnon and Stout in 1939 3 . In earlier experiments Arnon observed that minute amounts of molybdenum improved the growth of plants in solution culture 4 and that a group of seven heavy metals including .