Phosphorus & Phosphates

Langebaan Rock Phosphate - Langfos


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Langebaan Rock Phosphate (Langfos) is a phosphate rock (PR) of organic sedimentary origin that was widely marketed in South Africa until 1994. The original product Langfos Premium had a total phosphorus (P) concentration of 12.6% and citric P concentration of 3%, was milled and screened so that 80% of the particles passed through a 0.149mm sieve. The remainder of larger particles were used in combination with water soluble sources of superphosphate to manufacture granular NPK mixtures. In 2010 a new mine was opened and Langfos is once again available to farmers as an additional phosphate source for consideration. The total P content now ranges from 8 -10% and citric P concentration ranges from 1.8 -3.2%. 63% of the phosphate is in the tri calcium phosphate form and has a 20% calcium content as well as traces of Sulphur (S), Magnesium (Mg), Zinc (Zn), Boron (B), Copper (Cu), Molybdenum (Mo), Iron (Fe), Manganese (Mn) and Cobalt (Co). The product has a Group 2 Fertilizer registration in accordance with Act 36 of 1947. A comparison of Langfos Premium to the Langfos currently available:                                              Langfos Premium     Langfos                                              (Pre 1994)                      2010 – present Total P:                          12.6%                                8-10% Water soluble P:     0                                          0 Citric Soluble P:      3%                                      1.8-3.2% Particle size:             80% < 0.149mm          23% < 0.149mm 20% > 0.149mm           67% > 0.149mm  Langfos is not water soluble and should be considered to be a slow release fertilizer; approximately 50% of the P in Langfos becomes available for plant uptake in the first year of application, the balance over an extended period of time. From personal experience Langfos Premium has proven effective as a long term slow release source of P on acidic soils in Kwa Zulu Natal (KZN) and formed the basis of establishment of many Kikuyu pastures, sugarcane lands, avocado and citrus orchards where soil P test levels were found slowly increase despite limited or no application of superphosphate over periods spanning approximately 20 years. Thibaud et al. cite early researchers who found that the dissolution of PR is determined by gradients in the activities of phosphate, calcium, and hydrogen ions. The rate of PR decomposition is enhanced by soils with a low pH, high levels of reserve acidity and a low calcium status. PR was found to be more effective when applied to acid, well buffered soils than neutral soils and soils that had been recently limed. In addition to this soils with a large capacity to immobilize P from the soil solution generally promote more rapid and extensive dissolution of PR. Thibaud et al. (1992 & 1993) conducted research using a strongly P-fixing Balmoral clay and a weakly P-fixing Avalon sandy loam soil in greenhouse pot trails. They found that Langfos was not an effective substitute for superphosphate. It was however found that Langfos was more effective under strongly acidic conditions and that soils that retain P weakly may be more suited to fertilization with Langfos. The relative agronomic effectiveness (RAE) of Langfos compared to triple superphosphate however was 36% and 14%…

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