The Rural Voice, 1998-08, Page 55i
Advice
What kind of
deficiency is it?
By Keith Reid
Soil Fertility Specialist
Walkerton OMAFRA Office
More soybean fields than usual are
showing up with leaves turning
yellow while the veins stay green.
This is normally identified as
manganese deficiency, but the
symptoms also match the description
of iron deficiency. How do we sort
out which is which?
Plants require both iron and
manganese in small quantities. Iron is
required for the formation of
chlorophyll and is an activator in
processes like respiration and
photosynthesis. Manganese is an
activator in enzyme systems, and
assists iron in chlorophyll production.
Both are in the soil when pH is high.
The differences between iron and
manganese deficiency are subtle,
particularly in the early stages. In
more severe deficiencies, the veins of
iron deficient plants will turn yellow
as well as the inter -veinal tissue.
With manganese, no matter how
severely affected the area between
the veins is it will turn white in
severe cases, the veins will stay
green. How can we tell what is
manganese deficiency rather than
iron deficiency?
The first factor is the make-up of
our soils. We have a lot of iron in our
soils, the residue from the glaciers.
Even when the soil is quite alkaline,
this still leaves sufficient available
iron for crop growth.
The second factor is the history of
the fields. Most of the fields showing
yellow soybean leaves, also show
stunting and yellowing when they are
planted to cereals. Cereals are quite
sensitive to manganese deficiency,
but are insensitive to iron deficiency.
Manganese deficiency also shows
up on both eroded knolls and muck
hollows. Finally, in the past a foliar
spray of manganese has greened up
the fields with deficiency symptoms.
In short, when we see yellow
leaves with green veins, it is safe to
assume it is manganese deficiency.°
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AUGUST 1998 51