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  Section: Plant Nutrition » Macronutrients » Nitrogen
 
 
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Diagnosis of Nitrogen Status in Plants

 
     
 
Content
Determination of Essentiality
Nitrogen Metabolism and Nitrogenous Constituents in Plants
  Nitrate Assimilation
    - Nitrate Reductase
    - Nitrite Reductase
  Ammonium Assimilation
    - Glutamine Synthetase
    - Glutamate Synthase
    - Glutamic Acid Dehydrogenase
    - Transamination
    - Amidation
  Proteins and Other Nitrogenous Compounds
Diagnosis of Nitrogen Status in Plants
  Symptoms of Deficiency and Excess
  Concentrations of Nitrogen in Plants
    - Concentrations of Nitrogen in Plant Parts
    - Ratios of Concentrations of Nitrogen to Other Nutrients in Plants
Nitrogen in Soils
  Forms of Nitrogen in Soils
    - Organic Nitrogen in Soil
    - Inorganic Nitrogen in Soil
Soil Testing for Nitrogen
  Determinations of Total Nitrogen
  Biological Determinations of Availability Indexes
    - Determination of Inorganic Nitrogen
      - Ammonium
      - Nitrate
      - Amino Sugars
Nitrogen Fertilizers
  Properties and Use of Nitrogen Fertilizers
    - Anhydrous Ammonia: 82% N
    - Aqua Ammonia: 21% N
    - Urea: 46% N
    - Ammonium Nitrate: 34% N
    - Ammonium Sulfate: 21% N
    - Nitrogen Solutions: 28–32% N
    - Ammonium Phosphates: 10–21% N
    - Other Inorganic Nitrogen Fertilizers
    - Organic Nitrogen Fertilizers: 0.2–15% N
References
 
Symptoms of Deficiency and Excess
A shortage of nitrogen restricts the growth of all plant organs, roots, stems, leaves, flowers, and fruits (including seeds). A nitrogen-deficient plant appears stunted because of the restricted growth of the vegetative organs. Nitrogen-deficient foliage is a pale color of light green or yellow (Figure 2.1). Loss of green color is uniform across the leaf blade. If a plant has been deficient throughout its life cycle, the entire plant is pale and stunted or spindly. If the deficiency develops during the growth cycle, the nitrogen will be mobilized from the lower leaves and translocated to young leaves causing the lower leaves to become pale colored and, in the case of severe deficiency, to become brown (firing) and abscise. Until the 1940s crops received little nitrogen fertilizer (a typical application of N was 2 or 3 kg/ha), and when the light green color and firing appeared, farmers assumed that the soil was droughty (47).

Sometimes under conditions of sufficiency of nitrogen, leaves, especially the lower ones, will provide nitrogen to fruits and seeds, and symptoms of deficiency may develop on the leaves. These symptoms, which develop late in the growing season, may not be evidence of yield-limiting deficiencies but are expressions of transport of nitrogen from old leaves to other portions of the plant. For additional information on nitrogen-deficiency symptoms, readers should consult Cresswell and Weir (48–50), Weir and Cresswell (51,52) or Sprague (53).

Photographs of nitrogen deficiency symptoms on (a)</a> corn (Zea mays L.), (b) tomato (Lycopersicon esculentum Mill.), and (c) parsley (Petroselinum crispum Nym.).
FIGURE 2.1 Photographs of nitrogen deficiency symptoms on (a) corn (Zea mays L.), (b) tomato
(Lycopersicon esculentum Mill.), and (c) parsley (Petroselinum crispum Nym.).

At least 25%, more commonly more than 75%, of the nitrogen in leaves is contained in the chloroplasts (29,54). Most of the nitrogen of chloroplasts is in enzymatic proteins in the stroma and lamellae. Chlorophyll and proteins exist in lamellae as complexes referred to as chlorophyll proteins or holochromes (55–59). Nitrogen-deficient chloroplasts may be circular in profile rather than elliptical and may appear swollen. Nitrogen deficiency generally brings about a decrease in protein in chloroplasts and a degradation of chloroplast fine (lamellar) structure (60). Almost all membranous structure may be disrupted. Grana are often reduced in number or are indistinguishable. The loss of membranous structures is associated with the loss of proteins (61). A loss of chlorophyll occurs simultaneously with the loss of membranes and proteins, leading to the loss of green color from nitrogen-deficient leaves.





The loss of fine structure in chloroplasts during nutrient deficiency is not unique to nitrogen deficiency. Association of chloroplast aberrations with specific nutritional disorders has been difficult because of similarities in appearance of nutrient-deficient chloroplasts (62,63). The similarities are due to the effects that the deficiencies have on protein or chlorophyll synthesis (64,65). Elemental toxicities can also impart structural changes that resemble elemental deficiencies in chloroplasts (66).
 
     
 
 
     



     
 
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