Zinc deficiency

Generally, the first symptoms of zinc (Zn) deficiency in wheat appear on the middle-aged leaves, but considerable variation exists between individual plants; some plants produce symptoms in both old and middle-aged leaves simultaneously. These initial symptoms show a change in color from a healthy green to a muddy grey-green, generally in the central regions of the leaf. These leaf regions appear drought-stressed and necrotic areas beginning with a small necrotic spot soon develop, gradually extending to the margins.

As the deficiency becomes more severe, many leaves take on an oily appearance; the necrotic patches become larger and are surrounded by mottled yellow-green areas. At this stage, Zn-deficient leaves tend to collapse in the middle regions and even the youngest leaves produce symptoms.

Zn deficiency in wheat can occur in soils inherently low in Zn, in soils where Zn is unavailable to plants, and in soils where plant-available Zn has declined. Severe Zn deficiency in the field can result in stunted chlorotic plants with many collapsed leaves due to necrosis in the center of the leaves. Whole fields may be affected but, more generally, there are chlorotic patches within the crop.

Ordinary superphosphate may contain considerable Zn as a contaminant and dramatic effects of Zn deficiency can be seen on sandy soils when superphosphate is replaced by phosphatic fertilizers low in Zn.

Tolerance of cereals to Zn-deficient soils declines in the following order:

  • Rye (immune)
  • Triticale (mostly immune)
  • Bread wheat (highly variable)
  • Barley (highly variable)
  • Oats (sensitive)
  • Durum wheat (sensitive)

When soils are suspected of being severely Zn-deficient, durum wheat may be used as an indicator.

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