Sulphur (S) nutrition of crops has received a lot of attention since the advent of high grade phosphates and higher grade NPK fertilizer mixtures which typically contain very low levels of S. When considering your source of Sulphur (S) containing fertilizer, take time to assess the availability of the S sources that are available. Plants take up S in the Sulphate – SO42- form which is water soluble and immediately available for plant uptake while elemental S is not water soluble and must first be oxidized to the SO42- form by microbial action before becoming available for plant uptake. The oxidation rate of elemental S into the plant available SO42- form is also dependent on the particle size of the elemental S; the finer the particle size the quicker the conversion to the SO42- form. Granular elemental sources of S have been used in blends to “supply” the crops requirement, these granules don’t supply the crop’s immediate S requirement and can often be found encased in the soil or lying on the soil surface several years after application.
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…
Soil acidification is an unavoidable process that follows on from fertilization, different fertilizer products differ in their capacity to acidify the soil; substantial savings on lime costs can be made by selecting fertilizer products accordingly. Dr Erik Adriaanse explains how significant savings on lime costs may be achieved through the use of Limestone Ammonium Nitrate (LAN): Save on lime costs
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Dr Neil Miles consulting soil scientist
Neil Miles is a consulting soil scientist based in Mount Edgecombe. Prior to entering into consultancy, he spent 28 years with the KZN Department of Agriculture, as a research scientist and research manager, followed by 10 years in research and advisory work with the South African Sugarcane Research Institute (SASRI).
Neil played a leading role in the development of both the Cedara Fertilizer Advisory Service and SASRI’s Fertiliser Advisory Service (FAS). His PhD, through the University of Natal, focused on the nutrition of intensive pastures. Neil’s particular interests are soil health and the nutrition of crops and pastures.
Contact Neil: firstname.lastname@example.org