Agronomic Potential of Eleven Phosphate Rocks from Brazil, Colombia, Perú, and Venezuela1
- L. A. Léon,
- W. E. Fenster and
- L. L. Hammond2
The agronomic potential of 11 South American phosphate rocks was estimated by four laboratory methods (neutral ammonium citrate with two extractions, acid ammonium citrate [pH 3], 2% citric acid, and 2% formic acid) and by crop response data obtained from a greenhouse experiment with guinea grass (Panicum maximum Jacq.) on an acid (pH 4.9) Tropeptic Haplustox (Las Gaviotas) from Colombia. Standards for comparison included triple superphosphate (TSP) and phosphate rocks from the USA (North Carolina, central Florida, and Tennessee), Tunisia (Gafsa), and Israel (Arad). The relationship between laboratory reactivity values and crop response was evaluated following three cuttings of guinea grass at four rates of P application. Almost no yield was obtained without added P, and significant differences were observed between response curves of the P sources. Based on both solubility as measured by the four methods identified and crop response data, the 11 phosphate rocks were found to be segregated into four groups representing high (Bayovar), medium (Huila and Pesca), low (Sardinata, Patos de Minas, Lobatera, Araxá, and Abaeté), and very low (Catalão, Jacupiranga, and Tapira) reactivity. Solubility in neutral NH+4 citrate was found to be the most accurate of the chemical procedures tested. The relationship between yield and source solubility in neutral NH+4 citate showed that all of the sedimentary sources were more reactive than the igneous or metamorphic sources.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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