Fertilisers

What to read in the name of your granular fertiliser?

Het jy al gewonder wat die syfers op jou kunsmissak beteken?

An example of the many products available is 2:3:4(37)

The fertiliser in this example contains two parts Nitrogen, 3 parts phosphate and 4 parts potassium. The concentration is 37% (37% of the content is nutrients, 63% is inert).

The amount of nutrients in 2:3:4(37) can be calculated as follows:

% Nitogen (N) = [parts nitrogen/(parts nitrogen + phosphate + potassium)] x percentage = [2/(2+3+4)] x 37 = 8,2%.

% Phosphate (P) = [parts phosphate/(parts nitrogen + phosphate + potassium)] x percentage = [3/(2+3+4)] x 37 = 12,3%.

% Potassium (K) = [4/(2+3+4)] x 37 = 16,4%.

Dit is nou vir jou duidelik dat die syfers op die kunsmissak vir jou vertel hoeveel stikstof, fosfaat en kalium in jou kunsmis voorkom. Dit vertel ook vir my wat die verhoudings tussen die verskillende voedingstowwe is.

Indien jy ‘n kunsmis wil koop met meer stikstof as kalium, sal jy ‘n kunsmis kies waarvan die eerste syfer (stikstof) hoër is as die laaste syfer (K) (so ‘n tipe kunsmis sal jy byvoorbeeld vir grasperke en loof gebruik).

Indien jy ‘n kunsmis wil koop met meer kalium as stikstof, sal jy ‘n kunsmis kies waarvan die laaste syfer (kalium) hoër is as die eerste syfer (stikstof) (so ‘n tipe kunsmis sal jy byvoorbeeld vir groente gebruik).

Indien jy ‘n kunsmis wil koop met min fosfaat, sal jy ‘n kunsmis kies met ‘n middelste waarde van 0 of 1. Indien jy ‘n kunsmis wil koop met baie fosfaat, sal jy ‘n kunsmis kies met ‘n middelste waarde van 2 of meer.

Met ‘n bietjie dink en wiskunde kan jy nou ook uitwerk hoeveel kunsmis toegedien moet word om ‘n sekere hoeveelheid voedingstowwe toe te dien. Werk nou vir ons uit hoeveel 2:3:4(37) toegedien moet word as jy 2 gram stikstof op een vierkante meter wil toedien? E-mail die antwoord na florcom@icon.co.za.

An Example:

1. Non -soluble fertilisers:

  • Granular N-, P- and K- mixes:

These granular fertilisers consist of different ratios N:P:K. The ratio between the nutrients and the concentration of the nutrients are reflected in the name of the fertiliser.

An example of the many products available is 11:1:8(20)

The fertiliser in this example contains 11 parts N, 1 part phosphate and 8 parts potassium. The concentration is 20%.

Another example of the many products available is 3:1:5(36):

The fertiliser in example 2 contains three parts N, 1 part phosphate and 5 parts potassium. The concentration is 36%.

The amount of fertilisers in 3:1:5(36) can be calculated as follows:

% Nitogen = [3/(3+1+5)] x 36 = 12%.

% P = [1/(3+1+5)] x 36 = 4%.

% K = [5/(3+1+5)] x 36 = 20%.

Some suppliers have also added calcium, magnesium and trace elements.

  • Fertilisers containing phosphate:

Superphosphate contains 10,5% phosphate.

Dubbelsuperphosphate contains 19,6% phosphate.

Both these phosphate-containing fertilisers are not soluble. It is therefore necessary to incorporate it properly into the topsoil.

2. Water-soluble fertilisers

Names, formulations and characteristics of fertilisers

The most common water-soluble fertilisers are listed below:

1 2 3 4
Name Formulae Nutrient content (%) EC value (mS cm-1) at 250C.

Fertilisers containing calcium

Calcium Nitrate 5[Ca(NO3).2H2O].NH4NO3 15.5N; 19Ca; 1,24

Fertilisers containing potassium

Potassium Sulphate K2SO4 45 K; 18 S 1,54
Potassium Nitrate KNO3 13 N; 38 K 1,35

Fertilisers containing ammonium + nitrate

Ammonium Nitrate liquid NH4NO3 0,86

Fertilisers containing magnesium

Manganese Sulphate MnSO4.H2O 32 Mn
Magnesium Nitrate Mg(NO3)2.6H2O 11 N; 9 Mg

Fertilisers containing phosphate

Mono Potassium Phosphate KH2PO4 23 P; 28 K 0,68
Mono Ammonium Phosphate NH4H2PO4 27 P; 12 N 0,86

Fertilisers containing trace-elements

Manganese Sulphate MnSO4.H2O 32 Mn
Zinc Sulphate ZnSO4.7H2O 23 Zn
Borax Na2B4O7.10H20 11 B
Copper Sulphate CuSO4.5H2O 25 Cu
Sodium Molibdate Na2Mo4.2H2O 40 Mo
Iron chelate (13% EDTA) FE – EDTA 13 Fe
Iron chelate (11% DTPA) Fe – DTPA 11 Fe
Iron chelate (6% EDDHA) Fe – EDDHA 6 Fe

Column 1: These are the common names of the fertilisers.

Column 2: In this column the chemical formulae of each fertiliser is given.

Column 3: This is the amount of nutrients in the fertiliser.

Column 4: This is the electrical conductivity of one gram of the fertiliser if dissolved in one litre of distilled water.

3 Foliar feed:

Foliar feed contains macro elements, trace elements and sometimes also growth stimulants. An endless list of products is available.