Iron is most useful and useable to plant when
it occurs in soluble form. It is most soluble in the
pH range of 5 to 6.5. When the pH is outside of this
range, the resulting deficiency not only results in
an aesthetically displeasing plant, but it can have
economic impacts as well. Crop plants without
sufficient iron do not yield as much at harvest time,
and iron-deficient food crops often contain less
nutrition per unit than their iron-laden counterparts.
Iron Deficiencies
Iron deficiencies most often present themselves as
a yellowing (chlorosis) of the plant’s leaves. Many
other nutrient deficiencies also cause yellowing
leaves, so it is important to note where and how the
chlorosis appears. A plant lacking iron will show
its deficiency first in the younger leaves; in other
words, the new growth. When the deficiency first
appears, the entire leaf will not be yellow, but rather
the interveinal surface will still appear green. As
the problem continues or progresses, eventually the
entire leaf will turn yellow, even white in some plant
species. New growth, if it continues to be produced by
the plant, will be stunted. Eventually, brown lesions
may occur on the leaves and leaves will start to drop,
starting with the newer growth. In woody species
such as trees and shrubs, whole branches will begin
to die. Eventually, the entire plant can succumb to
iron deficiency and die in extreme cases.
By contrast, nitrogen deficiencies present themselves
as chlorosis on the plant’s older leaves first. Here, the
new growth takes the nitrogen from the older leaves.
Iron, on the other hand, is not so mobile within the plant
and leaves that have sufficient iron will hang on to it.
Iron deficiency can also be difficult to distinguish
from the symptoms of zinc deficiency. Zinc deficiency
presents almost identically to iron deficiency in both
color and location on the plant. The subtle difference
between the two conditions is that the interveinal
lesions on the leaf caused by a lack of zinc will be
slightly more rounded and the ones caused by a lack of
iron will be more angular. If unsure which deficiency is
present, take a sample to an experienced horticulturist
or your local cooperative extension for identification.
A more difficult to ascertain but nonetheless
present symptom of iron deficiency is to be found in
the root zone. For established plantings like trees
or shrubs, it is not practical and may do more harm
than good to dig out the plant to examine the roots.
However, in mass plantings such as with food crops,
this information is valuable. Plants absorb usable
iron towards the root tips. Depending upon the root
structure of the plant, this may be in the last inch to
few inches of root growth. An iron deficient plant will
likely have a stunted root system, which makes uptake
of iron difficult or impossible.
“Crop pla nts
with out suffi ci ent i ron do
not yi eld as much at h arvest
ti me, and i ron- defi ci ent food
crops often contai n less
nutriti on p er unit th an th ei r
i ron- laden counterp arts.”
grow cycle
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