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Secondary Nutrients
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Secondary Nutrients
Introduction
Calcium, magnesium and sulphur are considered as
secondary nutrients for plants; however, they play
no secondary role in plant nutrition.
They are just as essential for plant nutrition as
any of the other 14 essential plant nutrients.
Although, secondary nutrients are needed in
lesser amounts than that of primary nutrients but
they are important for plants.
They have been called the “synthesizers” because
of their functions in living organisms.
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Secondary Nutrients
Introduction
Many factors can affect the availability
of these three nutrients to plants.
The best estimates of their availability can be
determined by soil analysis or a combination
of soil and plant analyses.
However, field observations and deficiency
symptoms are also important diagnostic tools.
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Secondary Nutrients
Sulphur (S)
Sulphur is becoming more of a limiting nutrient in crop
production than in the past, for several reasons
Higher crop yields require more S
Increased use of high analysis fertilizers
containing little of no S
Reduced amounts of atmospheric S
fallout from the sky
Reduced soil S reserves from organic matter
losses due to mineralization and erosion.
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Secondary Nutrients
Sulphur (S)
Most S in the soil is tied up in organic matter and cannot
be used by the plant until it is converted to the sulphate
(SO4) form by soil bacteria. That process is known as
mineralization.
Sulphur can be applied as broadcast or banded
fertilizer material or applied through irrigation
systems (furrow and sprinkler).
Sulphur is also an important nutrient for proper
nutrition of forage crops that will be consumed by
livestock.
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Secondary Nutrients
Sulphur (S): Role in Plants
Sulphur (S) is an essential part of amino acids cysteine,
cystine and methionine. Hence, it is essential for protein
production.
S is involved in the formation of chlorophyll and
in the activation of enzymes. It is a part of the
vitamins biotin and thiamine (B1).
In most plants it makes up 0.2 to 0.3 per cent of dry
matter. Thus, it is as important in plant growth as
phosphorus and magnesium; but its role is often
underestimated.
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Secondary Nutrients
Sulphur (S): deficiency symptoms
As the supply of S becomes more limiting, young
leaves lack S and, hence, show deficiency
symptoms. In many ways, S deficiency
resembles that of N.
Unlike N deficiency, S-deficiency symptoms in
most cases appear first on the younger leaves,
and are present even after N application.
Plants deficient in S are small and spindly with
short and slender stalks. Their growth is
retarded, and maturity in cereals is delayed.
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Secondary Nutrients
Sulphur (S): Role in Plants
It is needed for the formation of mustard oils,
and the sulphydryl linkages that are the source
of pungency in onion, oils, etc.
S is required by
comparable with P.
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crops
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in
amounts
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Secondary Nutrients
Sulphur (S): deficiency symptoms
Nodulation in legumes is poor and N fixation is
reduced.
Fruits often do not mature fully and remain light
green in colour. Oilseed crops deficient in S
produce a low yield and the seeds have less oil
in them.
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Secondary Nutrients
Sulphur (S): deficiency symptoms
In Tomato
With Sulphur
Source:
http://5e.plantphys.net/image.php?id=373
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Without
Sulphur
Sources:
http://www.sulphurindia.com/Images/10.jpg
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Secondary Nutrients
Areas affected by deficiency (S)
Light textured soils with low organic matter
Canal irrigated areas
Areas where S-free fertilizers are used
Acid soils are more prone to S-deficiency due to
stronger adsorption of SO4.
Wheat is more prone to S deficiency than rice
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Secondary Nutrients
Sulphur Toxicity symptoms
S toxicity can occur under highly reduced
conditions, possibly as a result of sulphide
(H2S) injury.
Most plants are susceptible to high levels of
atmospheric SO2. Normal SO2 concentrations range
from 0.1 to 0.2 mg SO2/m3, and toxicity symptoms are
observed when these exceed 0.6 mg SO2/m3.
S-toxicity symptoms appear as necrotic spots on
leaves, which then spread over the whole leaf.
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Secondary Nutrients
Magnesium
Involved in phosphate metabolism, plant
respiration, and activation of enzyme systems.
Magnesium can be added to deficient soils by applying
Mg-containing fertilizers or dolomitic limestone.
Dolomitic limestone contains both Ca and Mg
carbonates (for neutralizing value), whereas
calcitic limestone contains only Ca carbonate.
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Secondary Nutrients
Magnesium
Availability of Mg is often related to soil pH.
Other situations also increase needs for Mg: .
sandy soils with low cation exchange capacity,
low Mg-supplying power, and a high
Mg leaching potential
application of calcitic limestone on low
Mg soils
crops with high Mg requirements; high
application rates of ammonium-N and K.
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Secondary Nutrients
Magnesium: role in plants
Mg ranks with Ca, P and S in the group of least
abundant macronutrients in plants.
Plants take up Mg in the form of Mg2+. Mg occupies the
centre-spot in the chlorophyll molecule and, thus, is vital
for photosynthesis.
It is associated with the activation of enzymes,
energy transfer, maintenance of electrical balance,
production
of
proteins,
metabolism
of
carbohydrates, etc. Mg is mobile within the plants.
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Secondary Nutrients
Magnesium: deficiency symptoms
As Mg is readily translocated from older to
younger plant parts, its deficiency symptoms
first appear in the older parts of the plant.
A typical symptom of Mg deficiency is the interveinal
chlorosis of older leaves in which the veins remain
green but the area between them turns yellow.
As the deficiency becomes more severe, the leaf
tissue becomes uniformly pale, then brown and
necrotic. Leaves are small and break easily (brittle).
Twigs become weak and leaves drop early.
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Secondary Nutrients
Magnesium: deficiency symptoms
Magnesium deficiency symptoms in maize
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Secondary Nutrients
Magnesium: deficiency symptoms
Magnesium
deficiency in tomato:
Source:
http://5e.plantphys.n
et/image.php?id=368
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Secondary Nutrients
Calcium
Calcium (Ca) is sometimes considered a “low
key” nutrient, but it carries a heavy load in plant
growth.
Calcium availability is adequate for most crops when
soils are limed to properly adjust soil acidity.
Deficiencies of Ca are most likely to occur on acid,
sandy soils from which available Ca has been leached
by rain or irrigation water, and on strongly acid peat
and muck soil where total soil Ca is low.
High exchangeable soil sodium (Na) may
depress plant uptake of Ca.
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Secondary Nutrients
Calcium: role in plants
Calcium (Ca) ranks with Mg, P and S in the group
of least abundant macronutrients in plants.
It is absorbed by plant roots as the divalent
cation Ca2+.
Ca is a part of the architecture of cell walls and
membranes.
It is involved in cell division, growth, root lengthening and
activation or inhibition of enzymes.
Ca is immobile in the phloem.
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Secondary Nutrients
Calcium: deficiency symptoms
Ca deficiency is seen first on growing tips and the
youngest leaves. This is the case with all nutrients that
are not very mobile in the plants.
Ca-deficient leaves become small, distorted, cupshaped, crinkled and dark green. They cease growing,
become disorganized, twisted and,under severe
deficiency, die.
Although all growing points are sensitive to Ca deficiency,
those of the roots are affected more severely.
Groundnut shells may be hollow or poorly filled as a
result of incomplete kernel development.
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Secondary Nutrients
Calcium: deficiency symptoms
Calcium deficiency in maize
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Calcium deficiency
in tomato
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Secondary Nutrients
Let us sum up
Secondary nutrients are considered secondary because while
they are essential to crop development, seasonal crop uptake
is usually lower than for the primary nutrients N,P, and K but
considerably higher than the micro-nutrients.
The secondary plant nutrients (calcium, magnesium
and sulphur) are equally important to the plant growth.
In case of their deficiency the plants will suffer.
The most common sources of calcium are gypsum and lime.
Gypsum is a mined product that contains both calcium and
sulphur, making it good for providing calcium.
Lime is available in the form of ground oystershells
and mined limestone.
A source of magnesium is magnesium sulphate, otherwise
known as epsom salts. Sulphur is available by itself in a
granulated form, and in ammonium sulphate, etc.
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