Calcium (Ca) & Magnesium (Mg)

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Role of calcium in plants

While calcium is considered a secondary plant nutrient, it plays a very important role in plant growth and nutrition, as well as in cell wall deposition. Calcium is necessary for the proper growth and functioning of root tips and meristems. It activates many plant enzyme systems, neutralises organic acids in the plant and increases the mechanical strength of the plant.

Calcium deficiency in wheat

  • Stunted roots (particularly lateral) that turn a dark colour and rot.
  • Leaves will not turn yellow, instead, old leaves will maintain dark green colour.
  • Necrotic spotting in the middle of the youngest leaf, leading to leaf collapse and unrolling.
  • Gelatinous wheat leaf tips and growing points.

Calcium deficiency in lupins

  • Shortening of lateral roots which then turn brown.
  • Leaflets of new leaves remain tightly closed.
  • Petioles of new leaves bend and collapse (leaves may only show a few chlorotic areas).
  • Bending of the main stem.
  • Necrotic tipping of unopened leaflets followed by the collapsing of the petioles.
  • New growing tips decay before any elongation of the petioles can occur.
  • Old and middle leaves become mottled and chlorotic, then die and shed.

Calcium deficiency in field peas

  • Stunted shoot and root growth.
  • Chlorotic crescent with small pink spots may appear at base of leaflets.
  • Young tendrils may wilt and collapse close to the junction of the main stem and the tendril.
  • Collapsing of petioles and leaves.
  • New leaves do not fully open and will curl along the margins with sharply pointed tips.
  • Old leaves remain healthy, dark green and fully formed.

Calcium deficiency in faba beans

In faba beans, a calcium deficiency affects the newest growth of the plant. Symptoms include:

  • Stems subtending new growth and the petiole of the youngest emerged leaf blade will collapse, then slowly turn black.
  • Leaf edges at the bottom end of very young leaves will curl inwards and exhibit a purplish necrosis, contrasting with the dark-green apex sections in the open region of the leaf.
  • Fully developed leaves feature purpling on the bottom end of the leaf, midrib and veins.

Role of magnesium in plants

Magnesium is an essential plant nutrient that plays a central role in plant photosynthesis. Without magnesium, chlorophyll cannot capture sun energy needed for photosynthesis. It also plays a significant part in transporting phosphorus, phosphate metabolism, plant respiration, protein synthesis, and the activation of several enzyme systems in the plant.

Causes of magnesium deficiency

An imbalance between calcium and magnesium in soils of low cation exchange capacity can worsen an existing magnesium deficiency. If the Ca:Mg ratio becomes too high in these soils, then plants may take up less magnesium. This may happen when a grower has used lime or gypsum on a soil relatively low in magnesium. Magnesium deficiency may also be worsened by high rates of potassium or high availability of ammonium-N.

Magnesium deficiency in wheat

  • New leaves will have a faded appearance followed by abnormal yellowing and twisted looking leaves (also seen in water stress).
  • Entire length of the leaves, including new shoots, may remain folded or rolled.
  • Blotches on yellowed new leaves, followed by death.
  • Mottled chlorosis and possibly reddish colouration around the outside of older leaves.

Magnesium deficiency in lupins

When magnesium deficiency symptoms first show up in lupins, no damage has yet occurred to the plant. Symptoms include:

  • Light green plants with some mild interveinal yellowing on old and new leaves.
  • Small bronze spots distributed randomly over the leaflet (spots do not merge to form necrosis).
  • Old leaves turn a dull greyish green, while new leaves arrange into clusters with dead tips.
  • Entire plant turns a dull green colour.

Magnesium deficiency in faba beans

Magnesium deficiency in faba Beans causes a variety of symptoms that cover leaves of all ages, after an initial stunting of growth. Symptoms include:

  • ‘Rolling in’ of the youngest leaves, persisting for the duration of the deficiency.
  • Umbrella-like folding back of middle leaflets.
  • Purple spotting on leaves.
  • Mottled chlorosis progresses into yellowing of area in between veins.
  • Reddish colour appearing on mottled leaves (middle – older leaves).
  • Dull red colour and pale necrosis appearing around leaf edges (younger leaves).

Magnesium deficiency in field peas

  • Presence of pink necrotic lesions between the midrib and the margins of leaves (old leaves will roll over the margins).
  • New leaves develop a pale green colour and plant growth is soon reduced.
  • Large areas of new leaves turn white and develop small pink necrotic spots.
  • New leaves lose all of their chlorophyll, are stunted and change to a narrow and pointed shape.
  • Old leaves take on a speckled chlorosis appearance with traces of pink areas.
  • Edges of all leaves, especially at the tip, roll over considerably.
  • Roots of plant remain healthy with good lateral root and root hair extension.

To find out more about preventing or correcting calcium or magnesium deficiency, speak to your local Area Manager.

Pasture
Soil Test Level
(K - ppm or mg/kg)
Cereals
Lupins
Canola*
Pulses
Low Rainfall
Medium Rainfall
High Rainfall
>120
0
0
0
0
0#
80 - 120
P.T.
0
0
10-20
20-30
60 - 80
15-20
0
10-20
20-30
30-40
40 - 60
20-25
P.T.
20-30
30-50
40-60
25-35
20-25
30-50
40-60
50-60
Product
Autumn Application
Winter Application
After 4 weeks
After 7 weeks
After 4 weeks
After 7 weeks
Amsul
3.7
6.9
1.0
2.5
Urea
59.9
58.4
36.8
38.9
Cations
Anions
Chemical Symbol & Charge
Name
Chemical Symbol & Charge
Name
K+
Potassium
NO3-
Nitrate
NH4+
Ammonium
Cl-
Chlorine
Na+
Sodium
SO4--
Sulphate
Cu++
Copper
HPO4- -
Phosphate
Zn++
Zinc
BO3----
Boron
Mn++
Manganese
MoO4- -
Molybdenum
Ca++
Calcium
Mg++
Magnesium
Fe++
Iron
N
P
K
S
Cu
Zn
Mn
Ca
Mg
Clover Pasture
25-30
3.5
16-20
2-3
0.005
0.02
0.40
0.4
1.2
Product
% N
Urea
46.0
MAXam/Amsul
21.0
UreaPlus
37.1
NitroPlus
33.4

Compounds

Product
%Ammonium-N
DAPSZC
16.4
MAPSZC
10.6
AllStar
13.0
Vigour
5.0
Product
N
P
K
S
Ca
Mg
Cu
Zn
Mn
kg per tonne
grams per tonne
Wheat
23
3
4
1.4
0.33
0.93
5
29
40
Barley
20
2.9
4.4
1.1
0.3
1.08
3
15
11
Oats
16
3
4
1.5
0.5
1.0
3
17
40
Canola
40
6.5
9.2
9.8
4.1
4.0
4
40
40
Lupins
51
3.8
8.8
3.1
1.7
1.7
5
30
60
Chickpeas
34
3.8
8.9
1.8
1.1
1.2
7
38
34
Faba Beans
39
3.8
9.8
1.4
1.1
1.0
10
28
30
Field Peas
37
4.0
8.2
2.0
0.7
1.2
5
35
14
Hay
20
2.0
25
2.0
0.5
1.1
5
20
40
Milk
5.7
0.95
1.4
0.3
1.2
0.12
Greasy Wool
170
0.26
15.8
28.5
1.2
0.3
Sheep - Live
34
7.0
2.3
4.0
14.4
0.4

Stubble

Product
N
P
K
S
Ca
Mg
Cu
Zn
Mn
kg per tonne
grams per tonne
Wheat
17
1.8
42
2.7
Canola
18
2.4
70
4.8
Lupins
17
0.6
26
2.7