Expert in the field of fertilizer, André Britz, has written an informative piece on buying fertilizer products, made available on

He writes:

What to expect when buying fertilizer products

Lees dit in Afrikaans

by André Britz, Pr.Sci.Nat.

Objective of fertilization

Provide nutrients (macro and micro elements) for plant production when lacking in soil Replace those nutrients removed by harvest and/or grazing Balancing nutrients for optimum yields of the best quality Sustainable farm enterprises and economic food production Meet growing demand for highly nutritious healthy food, that is safe for humans and animals, without harming to environment.

According to Act 36 (1947) in South Africa all raw materials in the fertilizer industry must be registered, which guarantees the buyer that the minimum requirements have been met. Registered products will bear a registration number [K/B] that is traceable. Such registrations are renewed every three years.

Features and benefits

The physical form of a fertilizer product or mixture (tailor-made blends are called ‘custom mix’) is required to be determined by the method of application or objective of fertilization as follows:

  • Granular and/or prill is meant for mechanical application, broadcast by a spreader or band placed by a planter (seeder). This includes subsoil applied by earthmoving machinery during soil preparation for deciduous fruit.
  • Granular contains the highest % concentration as homogenous ‘straights’ and NPK mixtures/compounds, to reduce transport costs and lower the volume applied on land.
  • Soluble (which can be a powder or crystalline) is dissolved in water. The N:P:K ratios can be determined on the farm.
  • Liquids can be handled mechanically using pumps or valves, with increased management and labour-efficiency. Due to explosive regulation of Ammonium Nitrate, it can only be utilised in a liquid form and/or lower concentration. Phosphoric acid as a liquid is one of the highest % Phosphate (P) sources.
  • Both soluble and liquid products can be applied through irrigation (fertigation) systems, for example drippers, micro or overhead sprinklers (pivot or linear). Fertilization is therefore directed to certain spot, a strip/band or otherwise limited area to prevent overdose or pollution. Every droplet presents the same ‘ratio’ and nutrient content, to ensure even distribution over the cropped area.
  • Foliar application is specifically directed at a target/deficient area and is often combined with crop protection solvents.

Nutrient content and attributes

  • Registered raw materials must comply with minimum nutrient levels and Potential Harmful elements prior to blending.
  • What is printed or claimed on the bag must be in the bag.
  • An Ammonium Nitrate product contains 50:50 Nitrate-N plus Ammonium-N, but no Ureic-N.
  • Liquids should have Specific Gravity (SG) to ease calibration calculations [as fertilizer weighs more than water]. The application of 100 kg of liquid product with SG = 1.2 results in applying 83 litres [100 ÷ 1.2 = 83].
  • Soluble products at 20 °C should fully dissolve in water.
  • The registration of raw materials is done in compliance with Potential Harmful elements (Table 12, Regulations of Act 36 (1947)).
  • The minimum to check 3.2.1 (30): 3 is Nitrogen (N), 3 ÷ (3+2+1) x 30 = 15% N 2 is Phosphate (P), 2 ÷ (3+2+1) x 30 = 10% P 1 is Potassium (K), 1 ÷ (3+2+1) x 30 = 5% K (30) Total nutrient content = 30% [NPK]


  • Granular products should maintain completeness until application (± 2-3 months post-bagging).
  • Particle size should be roughly: 5-10% > 4mm, 70-80% between 2 to 4mm, less than 5% < 2mm or dust (2mm diameter).
  • Packaging should prevent the contents from getting wet and protect it against other degradable materials (fuel, oils, etc.).
  • All packaging material is to be recycled.


  • Registered raw materials and/or mixtures are tested for minimum nutrient concentration and Potential Harmful elements.
  • Good Manufacturer Practices should be in compliance with Act 36 (1947).
  • Adhere to general regulations regarding handling and storage, the optimal utilisation of nutrients, prevent injury to personnel, and avoid pollution to the environment, foodstuff and water sources.

See the original post here.