beginner’s corner
A key point to remember when
evaluating chlorosis is that the lack of
iron, zinc, or manganese may cause the
chlorotic condition in a plant.”
A thorough analysis of all the factors
that may contribute to chlorosis is the
goal. We have a good idea of the most
likely suspects, so let’s see how this
malnutrition condition might get its
start. Understanding the most accu-
rate and comprehensive cause of a
plant malady leads us ultimately to the
proper treatment and cure.
Starting at the roots, our growing
medium is our fist place to look. Is it
capable of holding an adequate level of
the three vital micronutrients that affect
this condition? Looking at soils, there are
conditions that will make them unable to
hold or transport these minerals.
We need to consider the pH of that
soil. It turns out that each of the nutri-
ents we are discussing are adversely
affected by high pH. Iron easily reacts
with oxygen in the presence of high
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grow cycle
pH or very aerobic soils. When this
happens, it is quickly converted to iron
oxide, which is not plant available. You
can see that in grow medias with high
pH or those with high oxygen levels,
much of the available iron may not be
useful. Overly wet or cold soils will also
contribute to this issue, as will a soil
with high-clay content.
ENVIRONMENTAL STRESS
AND MICRONUTRIENTS
Environmental stress on the plant will
also affect the plant’s root system and
its ability to uptake micronutrients.
It is due to the plant’s immune or
self-protection system that this occurs,
as an overabundance of these miner-
als can be toxic. This response allows
the plant to reduce what it thinks may
be a nutrient overload. The presence
of higher levels of cadmium or cobalt
can also play a role in increasing iron
deficiency in plants.
Manganese (Mn) is present in soils
in three different states: Mn +2 , Mn +3 ,
and Mn +4 . It is this first state, Mn +2 , that
is plant available. When this form of
manganese is released in the soil and
present at the root surface, it is easily
diffused into the root. In the presence
of high pH, however, manganese can
precipitate into other chemical forms.
In the presence of very low pH soils
(below 5), manganese can become too
available and hence become toxic to
the plant. High organic matter can
also lead to trouble with the availabil-
ity of this mineral as the manganese
becomes easily chelated. In this case,
this process makes it less available
as dry soils reduce the availability of
manganese. Just to demonstrate the
complexity of maintaining availabil-
ity of this and many nutrients, a wet
and cold soil will reduce mineraliza-
tion (needed to produce Mn +2 ) of soil
organic matter as well as reduce root
growth and the metabolic activity of
the roots. It becomes apparent how the
grow media will affect availability of
these important minerals.