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NUTRIENT DEFICIENCY SYMPTOMS IN PLANTS Laboratory Exercise #12 OBJECTIVES Know the definition of element, compound, macronutrient and micronutrient. Know the 16 essential nutrient elements. Learn how to use the "Key to Nutrient Disorders ". INTRODUCTION Plants need at least 16 different chemical elements to grow. An element is a pure chemical that contains only one type of atom. Examples of common elements include iron, hydrogen, oxygen, nitrogen and carbon. Calcite, dolomite, and lime are examples of compounds. These substances consist of several elements bound together (e.g. CaCO3 or CaMg(CO3)2. Most minerals are compounds containing specific elements. The 16 elements required by plants are obtained from the soil, water and air. Thirteen of these elements must be supplied by the soil. Six of the soil elements required by plants are needed in relatively large amounts and are usually added to the soil through fertilizer or lime. These elements are termed macronutrients. The remaining 7 elements supplied by soil are required in very small amounts and are termed macronutrients. These elements are usually added as fertilizers because the soil is not always able to supply the amounts needed by plants. Table 1 lists the 16 essential plant elements and their chemical symbol. MEMORIZE ALL THESE ELEMENTS AND THE CHEMICAL SYMBOLS. Nutrient deficiency symptoms usually appear on the plant when one or more nutrients are in short supply. It is important to note the forms in which nutrients are taken up by the plant (Table 2). In many cases, deficiency may occur because an added nutrient is not in the form the plant can use. Deficiency symptoms for specific elements are included on the "Key to Nutrient Disorders". Every soil is not susceptible to the same nutrient deficiencies. For example, coarse-textured soils low in organic matter are susceptible to sulfur deficiencies whereas sulfur is usually in adequate supply in clayey soils or soils high in organic matter. Table 3 lists the soil conditions that lead to deficiencies of specific elements. Some crops are more susceptible to deficiencies of micronutrients than other crops. Listed in Table 4 are 6 micronutrients and the common plants that are susceptible to deficiencies in these elements. Table 1. Essential nutrient elements and their source Macronutrients Micronutrients Air and Water Soil Soil Carbon C Nitrogen N Iron Fe Hydrogen H Phosphorus P Manganese Mn Oxygen O Potassium K Boron B Calcium Ca Molybdenum Mo Magnesium Mg Copper Cu Sulfur S Zinc Zn Chlorine Cl Table 2. Forms of nutrients used by plants Nutrient Macronutrients Macronutrients Symbol Form Used by Plant Carbon C CO2 Hydrogen H H2O Oxygen O H2O Nitrogen N NH4+ & NO3 - Phosphorus P H2PO4 & HPO42- Potassium K K+ Calcium Ca Magnesium Mg Ca2+ Mg2+ Sulfur S SO42- Iron Fe Fe2+ Manganese Mn Mn2+ Boron B H2B03- Molybdenum Mo MoO42- Copper Cu Cu2+ Zinc Zn Zn2+ Chlorine Cl Cl- Cobalt Co Co2+ Nickel Ni Ni2+ Silicon Si Si(OH)4 Sodium Na Na+ Vanadium V V Beneficial Nutrients§ § May enhance the growth of some plants Table 3. Soil factors that may lead to deficiencies of selected nutrients. Element(s) Soil Factor Resulting in Deficiency N&K Excessive leaching on coarse-textured low organic matter soils P 1. Acid low organic matter soils 2. Cold wet soils such as occurs during early spring 3. Newly cleared soils S Excessive leaching on coarse-textured low organic matter soils in areas where air pollution is low (minimal levels of SO2 in the air) Ca & Mg 1. Excessive leaching on coarse-textured low organic matter soils 2. Soils where large amounts of K have been applied Fe 1. Poorly drained soils 2. Low organic matter soils, pH>7.0 3. Soils high in P Zn 1. Cold wet soils low in organic matter and highly leached 2. High pH soils (pH>7.0) 3. Soils high in P 4. Exposed subsoils Cu 1. Peat and muck soils 2. High pH, sandy soils 3. Soils heavily fertilized with N B 1. Excessive leaching on coarse-textured low organic matter soils 2. Soils with pH>7.0 Mn 1. Excessive leaching on coarse-textured low organic matter soils 2. Soil with pH>6.5 Mo 1. Soils high in Fe oxides, high adsorption of molybdenum 2. Soil cropped for a long time NOTE: Soil testing should be done to determine which nutrients are needed and how much of each should be applied. Excessive applications of the following nutrients may lead to toxicities: B, Cu, Fe, Mn and Zn. Table 4. Crops most likely to show micronutrient deficiencies. Micronutrient Susceptible Crop Mn Soybean, Small Grain & Peanuts Cu Wheat & Corn Zn Corn Mo Soybeans & Cauliflower B Alfalfa, Apples, Peanuts, Tobacco & Tomatoes Fe Ornamentals, Fruit Trees, Soybeans, Grain Sorghum & Some Grasses SLIDE SHOW The purpose of this lab is to become familiar with nutrient deficiencies in crops. When you see these symptoms on your own plants, you should get the soil tested to determine which nutrient is deficient and how much nutrient must be added to the soil to correct the problem. Take notes about the various deficiencies you observe in the slide show. Be prepared to identify the five unknown deficiencies shown at the end of the slide show. You may use the Key to Nutrient Disorders provided below. KEY TO NUTRIENT DISORDERS NITROGEN: General chlorosis. Chlorosis progresses from light green to yellow. Entire plant becomes yellow under prolonged stress. Growth is immediately restricted and plants soon become spindly and drop older leaves. PHOSPHORUS: Leaves appear dull, dark green, blue green, or red-purple, especially on the underside, and especially at the midrib and vein. Petioles may also exhibit purpling. Restriction in growth may be noticed. POTASSIUM: Leaf margins tanned, scorched, or have necrotic spots (may be small black spots which later coalesce). Margins become brown and cup downward. Growth is restricted and die back may occur. Mild symptoms appear first on recently matured leaves, then become pronounced .on older leaves, and finally on younger leaves. Symptoms may be more common late in the growing season due to translocation of K to developing storage organs. CALCIUM: Growing points usually damaged or dead (die back). Margins of leaves developing from the growing point are first to turn brown. MAGNESIUM: Marginal chlorosis or chlorotic blotches which later merge. Leaves show yellow chlorotic interveinal tissue on some species, reddish purple progressing to necrosis on others. Younger leaves affected with continued stress. Chlorotic areas may become necrotic, brittle, and curl upward. Symptoms usually occur late in the growing season. SULFUR: Leaves uniformly light green, followed by yellowing and poor spindly growth. Uniform chlorosis does not occur. COPPER: Leaves wilt, become chlorotic, then necrotic. Wilting and necrosis are not dominant symptoms. IRON: Distinct yellow or white areas appear between veins, and veins eventually become chlorotic. Symptoms are rare on mature leaves. MANGANESE: Chlorosis is less marked near veins. Some mottling occurs in interveinal areas. Chlorotic areas eventually become brown, transparent, or necrotic. Symptoms may appear later on older leaves. ZINC: Leaves may be abnormally small and necrotic. Internodes are shortened. BORON: Young, expanding leaves may be necrotic or distorted followed by death of growing points. Internodes may be short, especially at shoot terminals. Stems may be rough, cracked, or split along the vascular bundles. Study Questions 1. List all of the macronutrients which are supplied by the soil? 2. List all of the macronutrients which are not supplied by the soil? 3. List all of the micronutrients and their source? 4. What is the difference between macro and micronutrients? 5. In what form are nutrients taken up by plants? 6. Explain the role of pH and nutrient availability? 7. Many nutrients are mobile in the plant, how can you tell if the plant is deficient in mobile nutrients? 8. Other nutrients are not mobile, how can you tell if a plant is deficient in non-mobile nutrients?