| Both
soil testing and plant analysis can be useful in diagnosing
micronutrient deficiencies. Testing the soil for micronutrients
has become a widely-accepted practice in recent years.
However one must recognize that micronutrient soil tests
are not as reliable as the tests for soil acidity (pH)
or for phosphorus (P) and potassium (K) content. |
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| The
major limitation of current micronutrient soil testing
is that it measures only the quantity of nutrients present,
not their availability. Much work is still needed in correlating
soil micronutrient content with availability to the plant.
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| For
this reason plant analysis is also very important in deficiency
diagnosis. By combining plant analysis with soil tests
more accurate assessment of the micronutrient status of
soils and crops can be attained. |
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| There
are two ways to use plant analysis. One is to monitor
a crop's nutrient status; the other is to diagnose any
problem situations that might occur. |
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| As
a monitoring tool plant analysis can point out existing
or potential problems before visual symptoms develop.
Table 3 is a guide for sampling corn, soybeans small grain
and forage legumes including when to sample what plant
parts to collect and how much material is needed. While
analyses can be run on other plant parts and on samples
collected at other times the growth stages and plant parts
listed in the table allow for the most reliable readings.
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| Practice
good Field management |
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| Neither
the diagnosis of micronutrient deficiencies nor the treatment
to eliminate them is complex or expensive. Given the current
price of fertilizer land labor and other production inputs,
it makes sense to do everything possible to ensure that
the yield of your crop is not limited by a micronutrient
deficiency. Such a deficiency effectively wastes all the
dollar-expensive and energy-intensive inputs that we commit
to a crop today |
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| Attention
to the availability of micronutrients for field crops
is just good management! |
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| How
Soil Ph affects the availability of nutrients
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| Click
for enlarge view |
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Effects
of soil reaction on availability to plants of soil nutrients.
The width of the bar determines the relative availability
of each element
with a change in soil reaction. |
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| Micronutrient
Deficiency Symptoms |
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| Some
micronutrients have characteristic deficiency symptoms.
However, symptoms can be easily confused with other nutrient
deficiencies, salinity, disease, drought, herbicide injury
or other physiological problems. Visual symptoms alone
are not a reliable method of determining a micronutrient,
problem, but they are useful indicators when used with
other diagnostic tools. |
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| This
deficiency results in stunted growth of young plants.
The youngest leaves are affected first. They will be misshapen,
thick, brittle and small. Because boron is not easily
transferred from old to young leaves, older leaves usually
remain green and appear healthy. Often dark brown, irregular
lesions appear, followed by pale yellow chlorosis of young
leaves. Stems are short and growing points may die. In
canola, the symptoms of a boron deficiency can be confused
with a sulphur deficiency. In alfalfa, boron deficiency
symptoms include death of the terminal bud, rosetting,
yellow top and poor flowering. |
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| When
a boron deficiency is moderate, seed yield is often reduced
without any evidence of severe deficiency symptoms during
vegetative growth. |
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| Chlorine
deficiencies are very rare; therefore, symptoms are seldom
observed. Symptoms may include stubby roots, some chlorosis
of new leaves and plant wilting. |
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| Copper
is not readily transferred from old to young leaves, so
older leaves remain darker and relatively healthy and
the deficiency symptoms develop on younger leaves. The
visual symptoms of a copper deficiency in wheat include
yellowing of younger leaves, limpness, wilting, pigtailing
(whip tailing or curling) of the upper leaves and kinking
of the leaf tips. Other signs include excessive tillering,
aborted heads, delayed maturity and poor grain filling
resulting in a high straw to grain ratio. On copper deficient
soils these symptoms tend to occur in irregular patches.
Copper deficiency is often associated with the disease
stem or head melanosis and an increased incidence of ergot.
For barley, the symptoms of a copper deficiency include
yellowing, pigtailing, awn kinking, excessive tillering
and weak straw. Oats will also show pigtailing. Copper
deficiency symptoms have not been well documented for
canola or alfalfa. |
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| Chlorosis
of the younger leaves characterizes an iron deficiency.
The tissue between the veins gradually turns yellow, while
the veins tend to stay green. The tips and margins of
some leaves may turn brown and become dry and brittle.
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| In
legumes, deficiency symptoms include pale green young
leaves and a pale yellow mottling develops in interveinal
areas, while the veins remain green. Oats are an excellent
indicator crop. Manganese is partly mobile in oats. White
to grey flecks or specks first appear and become more
severe on mature leaves about halfway up the shoot. If
a deficiency persists, symptoms spread to old leaves then
to the youngest leaves. The specked condition is referred
to as "grey speck" and will appear in the interveinal
area of the lower half of older leaves and extend toward
the tip as symptoms develop. |
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| Manganese
is not readily transferred from old to young leaves in
wheat and barely. In wheat and barley, affected young
leaves frequently turn pale green and have a limp or wilted
appearance. A mild interveinal chlorosis develops in the
mid-section of the leaf and spreads rapidly becoming pale
yellow-green. Small white to grey spots, specks or strips
appear a short distance from the end of the leaf tip on
young leaves. |
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| Molybdenum
deficiency symptoms are similar to those of nitrogen.
Since molybdenum deficiencies are very uncommon symptoms
are rarely seen. |
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| Zinc
is partly mobile in wheat and barley. In these crops pale
yellow chlorotic areas appear on middle leaves, halfway
up the stem. Chlorotic symptoms first develop in the lower
half or mid-section of the leaf followed by grey or dark
brown necrosis of the leaf. Generally, stems are very
short and often fan-shaped with leaves crowded together
at the top. |
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| Zinc
deficient beans are stunted and older leaves are smaller
and narrower. The older leaves may have light blotches
between the veins. Younger leaves will have a more normal
healthy green color but may be smaller. |
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| In
flax, a zinc deficiency can cause grayish-brown spots
in the younger leaves with shortened internode spaces
and stunted appearance. |
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| In
corn, symptoms occur within a few weeks of emergence as
light yellow bands on the youngest leaves. The most severe
symptoms occur on the youngest leaves from the unfolding
bud, referred to as "white-bud". Old leaves
remain dark green and appear healthy. In a prolonged case
of deficiency the middle leaves develop pale yellow interveinal
chlorosis near the tips. A zinc deficiency prevents the
elongation of internodes and leaves, which results in
short stems with the leaves crowded together at the top
in a fan-shaped appearance. |
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| Note
that zinc deficiency symptoms are similar to those of
manganese and iron in some crops. |
