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There are twelve essential nutrients which plants must take up from the soil. For convenience, scientists have assigned symbols to each nutrient. Unfortunately, the fertilizer industry has developed an inconsistent way of measuring each nutrient, some as the element, some as the oxides.


Nutrient

Symbol

Method of measurement

Amount taken up (kg/ha)




6 tons corn

80 tons celery

Nitrogen

N

N

150

206

Phosphorus

P

P2O5

60

154

Potassium

K

K2O

120

240

Calcium

Ca

CaO

15

316

Magnesium

Mg

MgO

35

24

Sulphur

S

S

17


Iron

Fe

Fe

1.5


Manganese

Mn

Mn

0.4


Zinc

Zn

Zn

0.3


Boron

B

B

0.15


Copper

Cu

Cu

0.1


Molybdenum

Mo

Mo

0.01


Chlorine is also an essential nutrient, but not much attention has been paid to it until recently. There is a current debate as to whether silicon, nickel and cobalt are also essential nutrients.

The table above shows that plants need large amounts of N, P and K, therefore these nutrients are called MACRONUTRIENTS. They need smaller amounts of Ca, Mg and S and these are called SECONDARY NUTRIENTS. Fe, Mn, Zn, B, Cu and Mo are needed in very small amounts and are called MICRONUTRIENTS.

Although plants need more of some nutrients than others, they are all equally important. A shortage of any one will result in poor crop growth.

The table also shows that different plants require different amounts of each nutrient. This must be taken into account in making fertilizer recommendations.


What Nutrients Do Plants Need?