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  Section: Plant Nutrition » Macronutrients » Magnesium
 
 
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Assessment of Magnesium in Soils

 
     
 
Content
Historical Information
  Determination of Essentiality
Function in Plants
  Metabolic Processes
  Growth
  Fruit Yield and Quality
Diagnosis of Magnesium Status in Plants
  Symptoms of Deficiency and Excess
    - Symptoms of Deficiency
    - Symptoms of Excess
  Environmental Causes of Deficiency Symptoms
  Nutrient Imbalances and Symptoms of Deficiency
    - Potassium and Magnesium
    - Calcium and Magnesium
    - Nitrogen and Magnesium
    - Sodium and Magnesium
    - Iron and Magnesium
    - Manganese and Magnesium
    - Zinc and Magnesium
    - Phosphorus and Magnesium
    - Copper and Magnesium
    - Chloride and Magnesium
    - Aluminum and Magnesium
  Phenotypic Differences in Accumulation
  Genotypic Differences in Accumulation
Concentrations of Magnesium in Plants
  Magnesium Constituents
    - Distribution in Plants
    - Seasonal Variations
    - Physiological Aspects of Magnesium Allocation
  Critical Concentrations
    - Tissue Magnesium Concentration Associations with Crop Yields
    - Tabulated Data of Concentrations by Crops
Assessment of Magnesium in Soils
  Forms of Magnesium in Soils
  Sodium Absorption Ratio
  Soil Tests
  Tabulated Data on Magnesium Contents in Soils
    - Soil Types
Fertilizers for Magnesium
  Kinds of Fertilizers
  Effects of Fertilizers on Plant Growth
  Application of Fertilizers
References
 
Forms of Magnesium in Soils
Approximately 1.3, 4.7, and 4.3% of the earth's continental upper layer, lower layer, and the ocean crust is made up of magnesium, respectively (202). However, in surface soils, magnesium concentrations usually range from 0.03 to 0.84%, with sandy soils typically having the lowest magnesium concentrations (≈0.05%), and clay soils containing the highest magnesium concentrations (≈0.50%) (10,29). Like other metallic elements, the soil magnesium pool consists of three fractions: nonexchangeable, exchangeable, and water-soluble fractions. The nonexchangeable fraction consists of the magnesium present in the primary minerals and many of the secondary clay minerals (Table 6.2) (29). In many cases these compounds may be hydrated with one to several water molecules. The exchangeable fraction may make up approximately 5% of the total magnesium in the soil, accounting for 4 to 20% of the cation-exchange capacity of the soil (29). Magnesium concentrations in the soil solution typically range from 0.7 to 7.0mM, but may be as high as 100mM, with the soil solutions of acid soils generally having a lower magnesium concentration (about 2.0 mM) than soil solutions derived from neutral soils (about 5.0 mM) (29,203-207).



 
     
 
 
     



     
 
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