FAO - Plant Production and Protection DivisionFAO - Plant Production and Protection Division FAO Home Page
Plant Production and Protection Division Crop and Grassland Service FAO Home :: Agriculture 21 :: WAICENT
Mineral Fertilizer Specifications
 

Alternative crops
Production system
and biodiversity
Plant breeding
and biotechnology
Fertilizers and
plant nutrition
Good agricultural practises
Conservation agriculture
Urban/peri-urban
agriculture
Organic agriculture

 

Definitions

Many prefixes such as mineral, inorganic, or chemical are often used to describe fertilizers and these are used interchangeably.
Fertilizer grade is an expression referring to the legal guarantee of the available plant nutrients expressed as a percentage by weight in a fertilizer, e.g. a 12-32-16 grade of NPK complex fertilizer indicates the presence of 12 % nitrogen (N), 32 % phosphorous (P2O5) and 16 % potash (K2O). On a fertilizer bag, the NPK content is always written in the sequence N, P2O5, K2O.

Fertilizers are classified as

  • Straight fertilizers: These contain one of the 3 major nutrients N, P or K.
  • Compound /complex fertilizers: These contain at least two out of the three major nutrients.

Specifications/standards

Specifications against which commercial products are judged for quality. Specifications of several fertilizers have been developed in different countries.

For purchasing fertilizers from international and/or national markets, Specifications have to be indicated. Prices of specific type of fertilizer may differ according to the required quality and specification.

Toxicity

Adverse reaction of plants due to certain elements in soil or water which are taken up by plants and accumulated to a high concentration, resulting in plant damage or reduced yield.

Toxic elements

Elements which have a toxic or harmful effect on life of plants or micro-organisms. Elements associated with toxicity to plants are fluorine (F), aluminium (AL), lead (Pb), cadmium (Cd), chromium (Cr), selenium (Se), and mercury (Hg).

Heavy metals

An element having high atomic weight and specific gravity above 5. Most micronutrients are also heavy metals (such as: Fe, Mo, Mn, Ni, Cu, and Zn).

Threshold value

The concentration of a nutrient/element in the plant, soil or water above or below the optimum level for plant growth. The term is also used for indicating deficiency, toxicity or pollution levels.

Chelate

A metal-organic complex, in which a metal is bound by an organic chelating agent.
Some chelating agents are: EDTA, DTPA, EDDHA.
Example of chelated fertilizers containing micronutrients cations are: Zn-EDTA, Fe-EDTA.

 

Common Mineral Fertilizers

 

Fertilizer

%
N

%
P2O5

%
K2O

Nitrogen Fertilizers

 

 

 

1. Ammonium sulphate (NH4)2 SO4

21

 

 

2. Calcium nitrate Ca(NO3)2

16

 

 

3. Ammonium nitrate NH4NO3

35

 

 

4. Calcium ammonium nitrate NH4NO3 + CaCO3

27

 

 

5. Urea CO(NH2)2

46

 

 

Phosphate Fertilizers

 

 

 

6. Single superphosphate (SSP), CaH4(PO4)2+ CaHPO4· 2H2O

 

16-18

 

7. Triple superphosphate (TSP), Ca(H2PO4)2+ CaHPO4

 

46

 

8. Phosphate rock (PR), finely ground (< 0.16 mm)

 

22-40

 

9. Diammonium phosphate (DAP)

18

46

 

Potassium Fertilizers

 

 

 

10. Potassium chloride (MOP), KCl

 

 

60

11. Potassium sulphate (SOP), K2SO4

 

 

50

12. Potassium nitrate, KNO3

13

 

44

Compound Fertilizers(examples)

 

 

 

13. NPK

15

15

15

14. NPK

17

17

17

15. NPK

22

22

11

 

Fertilizer Specifications

1. Ammonium Sulphate

Moisture percent by weight, max. 1.0
Ammonical nitrogen percent by weight, min. 20.6
Free acidity (as H2SO4) 0.025
Arsenic (as As2O3) 0.01
Sulphur (as S) percent by weight, min. 23.0

 

2. Calcium Nitrate

Total nitrogen percent by weight, min. 15.5
Ammonical nitrogen percent by weight, max. 1.1
Nitrate nitrogen, as N percent by weight, min. 14.4
Water soluble calcium percent by weight, min. 18.8
Water insoluble Ca percent by weight, max. 1.5

 

3. Ammonium Nitrate

Total nitrogen percent by weight, min. 33.0
Ammonoical nitrogen percentage 50.0
Nitrate nitrogen percentage 50.0

 

4. Calcium Ammonium Nitrate

Moisture percent by weight 1.0
Total nitrogen, ammonical & nitrate %, min. 26.0
Calcium nitrate percent by weight, max.
Particle size: not less than 90 % shall pass through 4 mm IS sieve. Not more than 5 % shall be below 1 mm sieve.		 0.5

 

5. Urea (free flowing)

Moisture percent by weight, max. 1.5 (range from 0.5 - 1.5 %)
Total nitrogen percent by weight, min. 46.0
Biuret percent by weight, max. 1.5
Particle size: not less than 90 % shall pass through
2.8 mm sieve and not less than 80 % shall be retained on 1 mm IS sieve		  


5. Urea (granular)

Moisture percent by weight, max. 1.0 (range from 0.5 - 1.5 %)
Total nitrogen percent by weight, min. 46.0
Biuret percent by weight, max. 1.5
Particle size: not less than 90 % of the material shall pass through 4 mm IS sieve and not more than 5% shall be below 2 mm sieve  

 

6. Single Superphosphate

Moisture percent by weight, max. 12.0 (range from 4.5 - 12 %)
Free phosphoric acid (as P2O5) percent by weight, max. 4.0
Water soluble phosphate (as P2O5) percent by weight, min. 16.0
Sulphur (as S) percent by weight, min. 11.0

 

7. Triple Superphoshate

Moisture percent by weight, max. 12.0 (range from 3.5 - 12 %)
Free phosphoric acid (as P2O5) percent by weight, max. 3.0
Total phosphate (as P2O5) percent by weight, min. 46.0
Water soluble phosphate (as P2O5) percent by weight, min. 42.5

 

8. Phosphate Rock

Total phosphate (as P2O5) percent by weight, min.
But it can contain from 15 to 35 % P2O5		 18.0
Particle Size: min. 90 % of the material shall pass through 0.15 mm
IS sieve and the balance (10 %) shall pass through 0.25 mm sieve.		  
Cadmium content should not preferably exceed 27 mg/kg PR (= 90 mg Cd/kg P2O5)  

 

9. Diammonium Phosphate

Moisture percent by weight, max. 1.5 (range from 1.0 - 1.5 %)
Total N percent by weight, min. 18.0
Ammonical N percent by weight, min. 15.5
Total N in the form of Urea percent by weight, max. 2.5
Ammonium citrate soluble phosphate (as P2O5) percent by weight, min. 46.0
Water soluble phosphate (as P2O5) percent by weight, min.
Particle size:not less than 90 5 shall pass through 4 mm IS sieve
and not more than 5% shall be below 1mm. 		41.0

 

10. Potassium Chloride

Moisture percent by weight, max. 0.5
Water soluble potash content (as K2O) percent by weight, min. 60.0
Sodium (as NaCl) percent by weight, max. 3.5
Particle size: min. 65 % of material shall pass through 1.7 mm
sieve and be retained on 0.25 mm. 		 

 

11. Potassium Sulphate

Moisture percent by weight, max. 1.5 (range from 1.0 - 1.5 %)
Potash content as K2O percent by weight, min. 50.0
Total chloride as Cl percent by weight, max. 2.5
Sodium as NaCl percent by weight, max. 2.0
Sulphur as S percent by weight, min. 17.5

 

12. Potassium Nitrate

Moisture percent by weight, max. 0.5
Total N (nitrate form) percent by weight, min. 13.0
Water soluble potash (as K2O)percent by weight, min. 45.0
Sodium (as Na) percent by weight, max. 1.0
Total chloride (as Cl) percent by weight, max. 1.5

 

13. NPK, 15-15-15

Moisture percent by weight, max. 1.5 (range from 1.0 - 1.5 %)
Total nitrogen, min. 15.0
Ammonical N percent by weight, min. 12.0
Nitrogen in the form of urea, percent by weight, max. 3.0
Nitrate nitrogen percent by weight, max. 7.5
Neutral citrate soluble phosphates (as P2O5) percent by weight, min. 15.0
Water soluble phosphates (as P2O5) percent by weight, min. 12.0
Water soluble potash (as K2O) percent by weight, min.
Particle size: not less than 90% shall pass through 4 mm sieve and be retained on 1 mm IS sieve.
15.0
Calcium nitrate percent by weight, max. 1.0

 

14. NPK, 17-17-17

Moisture percent by weight, max. 1.5 (range from 1.0 - 1.5 %)
Total nitrogen percent by weight, min. 17.0
Ammonical nitrogen percent by weight, min. 5.0
Urea nitrogen percent by weight, max. 12.0
Neutral citrate soluble phosphates (as P2O5) percent by weight, min. 17.0
Water soluble phosphates (as P2O5) percent by weight, min. 14.5
Water soluble potash (as K2O) percent by weight, min.
Particle size: not less than 90% shall pass through 4 mm sieve and be retained on 1 mm IS sieve.		 17.0

 

15. NPK, 22-22-11

Moisture percent by weight, max. 1.5
Total nitrogen percent by weight, min. 22.0
Ammonical nitrogen percent by weight, min. 7.0
Urea nitrogen percent by weight, max. 15.0
Neutral citrate soluble phosphates (as P2O5) percent by weight, min. 22.0
Water soluble phosphates (as P2O5) percent by weight, min. 18.7
Water soluble potash (as K2O) percent by weight, min.
Particle size: not less than 90% shall pass through 4 mm sieve and be retained on 1 mm IS sieve. 		11.0

 

 

Micronutrient Fertilizers

1. Zinc Sulphate

Zinc (as Zn) percent by weight, min. 21.0
Lead (as Pb) percent by weight, max. 0.003
Copper (as Cu) percent by weight, max. 0.1
Magnesium (as Mg) percent by weight, max. 0.5
Sulphur (as S) percent by weight, min. 10.0
pH not less than 4.0
Cadmium (as Cd) percent by weight, max. 0.0025
Arsenic (as As) percent by weight, max. 0.01

 

2. Manganese Sulphate

Manganese (as Mn) percent by weight, min. 30.5
Lead (as Pb) percent by weight, max. 0.003
Copper (as Cu) percent by weight, max. 0.1
Magnesium (as Mg) percent by weight, max. 2.0
pH 3.75
Sulphur (as S) percent by weight, min. 17.0

 

3 . Borax (Sodium tetraborate)

Boron content (as B) percent by weight, min. 10.5
pH 9.0 - 9.5
Lead (as Pb) percent by weight, max. 0.003

 

4. Copper Sulphate

Copper (as Cu) percent by weight, min. 24.0
Lead (as Pb) percent by weight, max. 0.003
pH not less than 3.0
Sulphur (as S) percent by weight, min. 12.0

 

5. Ferrous Sulphate

Ferrous iron (as Fe) percent by weight, min. 19.0
Free acid (as H2SO4) percent by weight, max. 1.0
PH not less than 3.5
Lead (as Pb) percent by weight, max. 0.003
Sulphur (as S) percent by weight, min. 10.5

 

6. Chelated Zn, as Zn-EDTA

Zn content (as Zn) percent by weight, min. 12.0
Lead (as Pb) percent by weight, max. 0.003
pH 6.0 - 6.5

 

7. Chelated Iron, as Fe-EDTA

Iron content (as Fe) percent by weight, min. 12.0
Lead (as Pb) percent by weight, max. 0.003
pH 5.5 - 6.5

 

 

Heavy metals content in Phosphate Rock (PR)

Cadmium (Cd) is mobile in soils. It is potentially toxic element for animals and humans. It occurs in nature in the phosphate rocks. Its chemical separation is costly. Usual content in soils is about 0.4 ppm.

PR also contains several micronutrients, on average 42 ppm Cu, 90 ppm Mn, 7 ppm Mo, 32 Ni, and 300 ppm Zn.

Cd content in PR should not preferably exceed 27 ppm.

 

Examples of Phosphate Rock deposits containing high Cd

Morocco (Youssoufia)
120 ppm
Egypt
74 ppm
Tunisia (Gafsa)
173 ppm
Togo
147 ppm
Senegal (Taib)
221 ppm

Source: Demandt (1999), The world phosphate fertilizer industry, Institute for new technologies, Maastricht.

 

 

Average heavy metal concentration in PR deposits

PR Deposit

Heavy metal concentration, mg/kg

As

Cd

Cr

Pb

Hg

Ni

V

Russia (Kola)

1

0.1

13

3

0.01

2

100

United States

12

11

109

12

0.05

37

82

South Africa

6

0.2

1

35

0.06

35

3

Morocco

11

30

225

7

0.04

26

87

North Africa

15

60

105

6

0.05

33

300

Middle East

6

9

129

4

0.05

29

122

Average of 91 % of PR reserves,

4.8

10.9

82.0

4.4

0.02

12.6

38.4

mg/kg of P2O5

 

 

 

 

 

 

 

g/ha/yr applied with 20 kg P/ha

1

3.3

25

1

0.01

4

12

Tolerance limit in soil, mg/kg

-

2

100

100

2

50

50

Source: Kongshaug et al., 1992.

Furthermore some mineral fertilizers traditionally contain heavy metals and continuous yearly application can be harmful to both humans and the environment.

 

Contents of heavy metals in common mineral fertilizers (element content, ppm).

Fertilizer

Pb

Ni

Cu

Zn

Cr

Triple superphosphate

 

 

70

 

 

Ammonium sulphate

23

44

1

2

5

Calcium ammonium nitrate

21

13

4

13

8

Calcium nitrate

35

60

12

1

26

Urea

18

8

1

40

4


Source: Hilal et al, 1996

*In view of the concern regarding soil pollution/contamination from the application of fertilizer - containing heavy metals, the table below provides data on the levels of trace elements/heavy metals is soils, as reference material.

Common ranges and typical levels of trace elements in cultivated surface soils (mg/kg dry soil)

Element

Total content

Extractable content - normal range

 

Normal range

Typical

Using 0.5 mol/litre acetic acid

Using 0.05 mol/litre EDTA1

Ag

0.01 – 5

0.1

-

-

Al

10 000 – 50 000

70 000

50 – 2 600

50 – 2 000

As

0.1 – 40

6

-

-

Cd

0.01 – 1

0.5

< 0.01 – 0.3

< 0.01 – 0.3

Co

1 – 40

15

< 0.05 – 2.0

< 0.05 – 4.0

Cr

5 – 1 000

100

< 0.01 – 1.0

0.1 – 4.0

Cu

2 – 100

20

< 0.05 – 3.0

0.3 – 10

F

30 – 300

200

-

-

Fe

10 000 – 200 000

40 000

10–2 000

100 – 3 000

Hg

< 0.01 – 0.5

0.1

-

-

Li

5 – 200

50

-

-

Mn

100 – 4 000

800

5 – 100

5 – 100

Mo

0.2 – 5

2

< 0.004 – 0.03

0.03 – 1.0

Ni

5 – 500

50

0.1 – 5.0

0.2 – 5.0

Pb

2 – 200

20

< 0.002 – 4.0

1.0 – 10.0

 

 

 

-

-

 

 

 

-

-

Se

0.1 – 2.0

0.5

-

-

Sn

<1 – 10

3

< 0.02 – 0.2

< 0.02–1.0

 

 

 

 

 

Ti

1 000–20 000

4 000

< 0.1 – 1.0

0.5 – 10

Y

3 – 150

40

-

-

Zn

10 – 300

50

< 2 – 30

< 3 – 20

Zr

60 – 2 000

400

-

-

1 Ethylenediamine tetra-acetic acid

Source: Berrow and Burridge, 1980.

     
© FAO AGP (2007) Contact webmaster Last update: 27 March 2007   Top