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NPK Products

FERTILIZER GRADES AND NUTRIENT CONCENTRATIONS IN RSA AND SADC COUNTRIES

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All fertilizer products sold in South Africa must be registered in terms of the Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act 36 of 1947) and are sold with a specific registered plant nutrient concentration which is printed on the fertilizer packaging. The South African fertilizer industry manufactures a broad range of fertilizer products as compounds or mixtures which contain two or more of the Primary Macro plant nutrients Nitrogen (N), Phosphorus (P) and Potassium (K) which are broadly referred to as NPK products. In South Africa NPK products are named using a numerical system e.g. 4:3:4(33) which is called the “grade” of the product. The grade of a product is also a guarantee of analysis for that specific product; the tolerance on nutrient concentration variances in a product are regulated by Act 36 of 1947. The grade 4:3:4(33)  contains the primary macro nutrients in a ratio of 4 parts N : 3 parts P : 4 parts K, the sum of which totals 11 parts.The total plant food concentration is displayed in brackets, in this example 33%.  The NPK concentrations can be calculated from the grade accordingly: The concentration of N: 4⁄11 X 33 = 12% The concentration of P: 3/11 X 33 = 9% The concentration of K: 4⁄11 X 33 = 12% The total nutrient concentration of NPK adds up to 33% as displayed in brackets. The other 67% of the product consists of the elements Ca, H, O, S, Cl and a few other elements which are constituents of the raw material compounds and filler material. Other Secondary Macro Nutrients such as Sulphur (S) and micro nutrients such as Zinc (Zn) may also be registered as plant food ingredients in NPK products; their concentrations are expressed as a percentage and included in the grade notation of the product, e.g.: 4:3:4(33)+0.5%Zn or 4:3:4(33) +2% S +0.5%Zn. In some SADC countries, Europe and America fertilizer grades are expressed differently, where all the numbers in the grade refer to percentages of plant nutrient however the P and K content are expressed as oxides: Total N is as % N Total P is as % P2O5 Total K is as % K20 To convert P2O5 to % P multiply by 0.4364 (conversely divide by 2.2915) To convert K2O to % K multiply by 0.8302 (conversely divide by 1.2046) For example the Zambian product with the grading 8: 24: 16 would contain elemental nutrient concentrations equating to: N: 8% P: 24 X 0.4364 = 10.47% K: 16 X 0.8302 = 13.28% Please note: Consult a qualified person (Act 36 of 1947) for specific applications / recommendations.

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Filler material

FERTILIZER AND FILLER MATERIAL

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The South African fertilizer industry manufactures a broad range of NPK fertilizer products which are typically mixtures of two or more chemical compounds (raw materials) such as Limestone Ammonium Nitrate (LAN), Ammonium Sulphate, Mono Ammonium Phosphate (MAP), Potassium Chloride and Urea. All fertilizer products sold in South Africa must be registered in terms of the Fertilizers, Farm Feeds, Agricultural Remedies and Stock Remedies Act, 1947 (Act 36 of 1947) and are sold with a specific registered plant nutrient concentration which is printed on the fertiliser packaging. Not all of the constituents of the fertiliser raw materials used to manufacture NPK mixtures are plant nutrients (i.e. nitrogen (N), phosphorus (P) and potassium (K)). For example: LAN has a N content of 28%, the remaining 72% consists of hydrogen (H), oxygen (O) and approximately 21% limestone which acts as a carrier of the plant food. Ammonium Sulphate consists of 21% N, 24% sulphur and the remaining 55% consists of H and O. Potassium Chloride typically has a K content of 51% while the remaining 49% consists of chlorine. MAP consists of 11% N, and 22% P; the remaining 67% consists of H, O and carrier material. Urea consists of 46% N, the remaining 54% consists of C, H and O. All fertiliser products / raw materials are produced on large scale through industrial processes and are manufactured to the specification of their registrations in terms of Act 36 of 1947. Due to the nature of these processes it is normal that slight variances occur in the production process bringing about a slight variance in the concentration of plant nutrients in the different batches of product that are manufactured. The tolerance on concentration variance both upwards and downwards of a product is regulated by Act 36 of 1947. When raw materials are subsequently used to manufacture NPK mixtures, the variances in the plant nutrient content of the raw materials will have an impact on the final plant nutrient content of the NPK mixture. In order to ensure that NPK mixtures consistently meet specification, NPK mixtures are typically formulated to carry in the region of 1-2% filler material. All raw materials used in the production of NPK mixtures are analyzed on a continuous basis and where necessary the bill of materials for a specific product is adjusted to ensure that the final NPK product meets specification. In the event that one or more of the raw materials to be used has a plant nutrient concentration towards the lower end of the specification allowed for the raw material, the addition of filler will be reduced. Similarly, in the event that if the raw materials to be used have a plant nutrient concentration towards the upper end of the specification allowed for the raw material, the filler content may be increased. The filler material that is used in the production of mixtures is typically a course sand which is screened to ensure that 90% of the particle sizes range between 2.00 – 4.00 mm; it has…

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