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Absence or insufficiency of
iron needed for normal growth and development. |
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Iron deficiency , or lime-induced
chlorosis, is often caused by an alkaline soil (high pH). As the pH
of the soil increases above 6.0, the availability of iron to the
plant gradually decreases. A wide range of ornamentals including
both Australian native plant species and introduced species is
affected by iron chlorosis .
Importance of iron
Iron is needed by all plants. It is an essential precursor for the
formation of chlorophyll, which gives plant foliage its green
colour. Chlorophyll is an active element in photosynthesis, a
process which allows the plant to grow, mature and produce flowers.
Iron is also important for normal activity of enzymes involved in
plant respiration.
Symptoms of iron deficiency
Plant growth and vigour are reduced when the iron supply is limited.
Since iron is not easily translocated within the plant, the symptoms
of reduced green colour, due to less chlorophyll production, appear
on the new leaves. The visual symptom on these new leaves is
interveinal chlorosis, or yellowing of the plant between the leaf
veins. In severe cases the entire leaf may be white. This symptom is
similar to that caused by magnesium deficiency but iron deficiency
is exhibited on the younger leaves, while magnesium deficiency is
exhibited on the older leaves. Symptoms of iron deficiency tend to
be more pronounced during winter.
Causes of iron deficiency
Iron deficiency does not only occur in alkaline soils but very often
develops in acid soils, frequently limiting the growth of such
acid-loving species as azaleas and rhododendrons. This condition may
result from an accumulation of the heavy metals, copper, manganese
and zinc, relative to the amount of iron present.
Other factors, which may cause iron to become unavailable for
plant use, are:
- high levels of calcium and magnesium carbonate
- overwatering of plants, causing poor aeration
- high or low temperature
- root damage
- large amounts of bicarbonate ions in soil solution or
irrigation water
- high nitrate nitrogen in fertilisers
- high phosphate levels
- a deficiency of iron itself.
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